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Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
Azure Synapse Analytics
SQL database in Microsoft Fabric
Creates a relational index on a table or view. Also called a rowstore index because it is either a clustered or nonclustered B-tree index. You can create a rowstore index before there is data in the table. Use a rowstore index to improve query performance, especially when the queries select from specific columns or require values to be sorted in a particular order.
Note
Documentation uses the term B-tree generally in reference to indexes. In rowstore indexes, the Database Engine implements a B+ tree. This does not apply to columnstore indexes or indexes on memory-optimized tables. For more information, see the SQL Server and Azure SQL index architecture and design guide.
Azure Synapse Analytics currently doesn't support unique constraints. Any examples referencing unique constraints are only applicable to SQL Server, Azure SQL Database, SQL database in Microsoft Fabric, and Azure SQL Managed Instance.
For information on index design guidelines, refer to the SQL Server index design guide.
Examples:
Create a nonclustered index on a table or view
CREATE INDEX index1 ON schema1.table1 (column1);Create a clustered index on a table and use a 3-part name for the table
CREATE CLUSTERED INDEX index1 ON database1.schema1.table1 (column1);Create a nonclustered index with a unique constraint and specify the sort order
CREATE UNIQUE INDEX index1 ON schema1.table1 (column1 DESC, column2 ASC, column3 DESC);
Key scenario:
Starting with SQL Server 2016 (13.x), in Azure SQL Database, SQL database in Microsoft Fabric, and in Azure SQL Managed Instance, you can use a nonclustered index on a columnstore index to improve data warehousing query performance. For more information, see Columnstore indexes - data warehouse.
For additional types of indexes, see:
Transact-SQL syntax conventions
Syntax
Syntax for SQL Server, Azure SQL Database, SQL database in Fabric, Azure SQL Managed Instance
CREATE [ UNIQUE ] [ CLUSTERED | NONCLUSTERED ] INDEX index_name
ON Backward compatible relational index
Important
The backward compatible relational index syntax structure will be removed in a future version of SQL Server.
Avoid using this syntax structure in new development work, and plan to modify applications that currently use the feature.
Use the syntax structure specified in
CREATE [ UNIQUE ] [ CLUSTERED | NONCLUSTERED ] INDEX index_name
ON Syntax for Azure Synapse Analytics
CREATE CLUSTERED COLUMNSTORE INDEX index_name
ON [ database_name . [ schema ] . | schema . ] table_name
[ORDER (column[,...n])]
[WITH ( DROP_EXISTING = { ON | OFF } )]
[;]
CREATE [ CLUSTERED | NONCLUSTERED ] INDEX index_name
ON [ database_name . [ schema ] . | schema . ] table_name
( { column [ ASC | DESC ] } [ ,...n ] )
WITH ( DROP_EXISTING = { ON | OFF } )
[;]
Arguments
UNIQUE
Creates a unique index on a table or view. A unique index is one in which no two rows are permitted to have the same index key value.
The Database Engine doesn't allow creating a unique index on columns that already include duplicate values, whether or not IGNORE_DUP_KEY is set to ON. If this is attempted, the Database Engine displays an error message. Duplicate values must be removed before a unique index can be created on the column or columns.
A UNIQUE constraint treats NULL as a value. If a column is nullable and a UNIQUE constraint exists on the column, at most one row with a NULL is allowed.
CLUSTERED
Creates an index in which the sort order specified for the index key columns determines the page order in the index structure on disk. Rows on the pages in the bottom, or leaf, level of the clustered index always contain all columns of the table. Rows on the pages in the upper levels of the index contain key columns only.
A table can have only one clustered index. If a clustered index exists on a table, it contains all data in the table. A table without a clustered index is called a heap.
A view with a unique clustered index is called an indexed view. An indexed view can have only one clustered index. Creating a unique clustered index on a view physically materializes the view. A unique clustered index must be created on a view before any other indexes can be defined on the same view. For more information, see Create indexed views.
Create the clustered index before creating any nonclustered indexes. Existing nonclustered indexes on tables are rebuilt when a clustered index is created, which is a resource-intensive operation if the table is large.
If CLUSTERED isn't specified, a nonclustered index is created.
Note
Because the clustered index contains all data in the table, creating a clustered index and using the ON partition_scheme_name or ON filegroup_name clause effectively moves the table from the filegroup on which the table was created to the new partition scheme or filegroup. Before creating tables or indexes on specific filegroups, verify which filegroups are available and that they have enough empty space for the index.
In some cases, creating a clustered index can enable previously disabled indexes. For more information, see Enable indexes and constraints and Disable indexes and constraints.
NONCLUSTERED
Creates an index in which the sort order specified for the index key columns determines the page order in the index structure on disk. Unlike the clustered index, rows on the pages in the leaf level of a nonclustered index contain only the index key columns. Optionally, a subset of non-key columns can be included using the INCLUDE clause.
Each table can have up to 999 nonclustered indexes, regardless of how the indexes are created: either implicitly with the PRIMARY KEY and UNIQUE constraints, or explicitly with CREATE INDEX.
For indexed views, nonclustered indexes can be created only on a view that has a unique clustered index already defined.
If not otherwise specified, the default index type is nonclustered.
index_name
The name of the index. Index names must be unique within a table or view, but don't have to be unique within a database. Index names must follow the rules of identifiers.
column
The column or columns on which the index is based. Specify two or more column names to create a composite index on the combined values in the specified columns. List the columns to be included in the composite index, in sort-priority order, inside the parentheses after table_or_view_name.
Up to 32 columns can be combined into a single composite index key. All the columns in a composite index key must be in the same table or view. The maximum allowable size of the combined index values is 900 bytes for a clustered index, or 1,700 for a nonclustered index. The limits are 16 columns and 900 bytes for versions before SQL Database and SQL Server 2016 (13.x).
Columns that are of the large object (LOB) data types ntext, text, varchar(max), nvarchar(max), varbinary(max), xml, or image can't be specified as key columns for an index. Also, an indexed view definition can't include ntext, text, or image columns, even if they are not referenced in the CREATE INDEX statement.
You can create indexes on CLR user-defined type columns if the type supports binary ordering. You can also create indexes on computed columns that are defined as method invocations off a user-defined type column, as long as the methods are marked deterministic and don't perform data access operations. For more information about indexing CLR user-defined type columns, see CLR user-defined types.
[ ASC | DESC ]
Determines the ascending or descending sort direction for the particular index column. The default is ASC.
INCLUDE (column [ ,... n ] )
Specifies the non-key columns to be added to the leaf level of a nonclustered index. The nonclustered index can be unique or non-unique.
Column names can't be repeated in the INCLUDE list and can't be used simultaneously as both key and non-key columns. Nonclustered indexes always implicitly contain the clustered index columns if a clustered index is defined on the table. For more information, see Create indexes with included columns.
All data types are allowed except text, ntext, and image. Starting with SQL Server 2012 (11.x), in Azure SQL Database, SQL database in Microsoft Fabric, and in Azure SQL Managed Instance, if any one of the specified non-key columns are varchar(max), nvarchar(max), or varbinary(max) data types, the index can be built or rebuilt using the ONLINE option.
Computed columns that are deterministic and either precise or imprecise can be included columns. Computed columns derived from image, ntext, text, varchar(max), nvarchar(max), varbinary(max), and xml data types can be included as long as the computed column data type is allowable as an included column. For more information, see Indexes on computed columns.
For information on creating an XML index, see CREATE XML INDEX.
WHERE
Creates a filtered index by specifying which rows to include in the index. The filtered index must be a nonclustered index on a table. Creates filtered statistics for the data rows in the filtered index.
The filter predicate uses simple comparison logic and can't reference a computed column, a user-defined data type (UDT) column, a spatial data type column, or a hierarchyid data type column. Comparisons with NULL literals using the comparison operators are not allowed. Use the IS NULL and IS NOT NULL operators instead.
Here are some examples of filter predicates for the Production.BillOfMaterials table:
WHERE StartDate > '20000101' AND EndDate <= '20000630'
WHERE ComponentID IN (533, 324, 753)
WHERE StartDate IN ('20000404', '20000905') AND EndDate IS NOT NULL
Filtered indexes don't apply to XML indexes and full-text indexes. For UNIQUE indexes, only the selected rows must have unique index values. Filtered indexes don't allow the IGNORE_DUP_KEY option.
ON partition_scheme_name ( column_name )
Specifies the partition scheme that defines the filegroups onto which the partitions of a partitioned index are mapped. The partition scheme must exist within the database by executing either CREATE PARTITION SCHEME or ALTER PARTITION SCHEME. column_name specifies the partitioning column for the index. This column must match the data type, length, and precision of the argument of the partition function that partition_scheme_name is using. column_name isn't restricted to the columns in the index definition. Any column in the base table can be specified, except when partitioning a unique index, column_name must be chosen from among those used as the unique key. This restriction allows the Database Engine to verify uniqueness of key values within a single partition only.
Note
When you partition a non-unique, clustered index, the Database Engine by default adds the partitioning column to the list of clustered index keys, if it is not already specified. When partitioning a non-unique, nonclustered index, the Database Engine adds the partitioning column as a non-key (included) column of the index, if it is not already specified.
If partition_scheme_name or filegroup isn't specified and the table is partitioned, the index is placed in the same partition scheme, using the same partitioning column, as the underlying table.
Note
You cannot specify a partitioning scheme on an XML index. If the base table is partitioned, the XML index uses the same partition scheme as the table.
For more information about partitioning indexes, Partitioned tables and indexes.
ON filegroup_name
Creates the specified index on the specified filegroup. If no location is specified and the table or view isn't partitioned, the index uses the same filegroup as the underlying table or view. The filegroup must already exist.
ON [default]
Creates the specified index on the same filegroup or partition scheme as the table or view.
The term default, in this context, isn't a keyword. It is an identifier for the filegroup or partitioned scheme of the table or view and must be delimited, as in ON "default" or ON [default]. If "default" is specified, the QUOTED_IDENTIFIER option must be ON for the current session. This is the default setting. For more information, see SET QUOTED_IDENTIFIER.
Note
In the context of CREATE INDEX, "default" and [default] don't indicate the database default filegroup. They indicate the filegroup or partition scheme used by the base table or view. This differs from CREATE TABLE, where "default" and [default] place the table on the database default filegroup.
[ FILESTREAM_ON { filestream_filegroup_name | partition_scheme_name | "NULL" } ]
Specifies the placement of FILESTREAM data for the table when a clustered index is created. The FILESTREAM_ON clause allows FILESTREAM data to be moved to a different FILESTREAM filegroup or partition scheme.
The filestream_filegroup_name is the name of a FILESTREAM filegroup. The filegroup must have one file defined for the filegroup by using a CREATE DATABASE or ALTER DATABASE statement; otherwise, an error is raised.
If the table is partitioned, the FILESTREAM_ON clause must be included and must specify a partition scheme of FILESTREAM filegroups that uses the same partition function and partition columns as the partition scheme for the table. Otherwise, an error is raised.
If the table isn't partitioned, the FILESTREAM column can't be partitioned. FILESTREAM data for the table must be stored in a single filegroup that is specified in the FILESTREAM_ON clause.
FILESTREAM_ON NULL can be specified in a CREATE INDEX statement if a clustered index is being created and the table doesn't contain a FILESTREAM column.
For more information, see FILESTREAM (SQL Server).
The fully qualified or nonfully qualified object to be indexed.
database_name
The name of the database.
schema_name
The name of the schema to which the table or view belongs.
table_or_view_name
The name of the table or view to be indexed.
To create an index on a view, the view must be defined with SCHEMABINDING. A unique clustered index must be created on a view before any nonclustered index is created. For more information about indexed views, see Remarks.
Starting with SQL Server 2016 (13.x), the object can be a table stored with a clustered columnstore index.
Azure SQL Database supports the three-part name format tempdb and # or ##. If the schema name is dbo,
::=
Specifies the options to use when you create the index.
PAD_INDEX = { ON | OFF }
Specifies index padding. The default is OFF.
ON
The percentage of free space that is specified by fill factor is applied to the intermediate-level pages of the index. If
FILLFACTORisn't specified at the same timePAD_INDEXis set toON, the fill factor value in sys.indexes is used.OFF
The intermediate-level pages are filled to near capacity, leaving sufficient space for at least one row of the maximum size the index can have, considering the set of keys on the intermediate pages. This also occurs if
PAD_INDEXis set toONbut fill factor isn't specified.
The PAD_INDEX option is useful only when FILLFACTOR is specified, because PAD_INDEX uses the percentage specified by FILLFACTOR. If the percentage specified for FILLFACTOR isn't large enough to allow for one row, the Database Engine internally overrides the percentage to allow for the minimum. The number of rows on an intermediate index page is never less than two, regardless of how low the value of FILLFACTOR.
In backward compatible syntax, WITH PAD_INDEX is equivalent to WITH PAD_INDEX = ON.
FILLFACTOR = fillfactor
Specifies a percentage that indicates how full the Database Engine should make the leaf level of each index page during index creation or rebuild. The fillfactor value must be an integer value from 1 to 100. Fill factor values 0 and 100 are the same in all respects. If fillfactor is 100, the Database Engine creates indexes with leaf pages filled to capacity.
The FILLFACTOR setting applies only when the index is created or rebuilt. The Database Engine doesn't dynamically keep the specified percentage of empty space in the pages.
To view the fill factor setting, use the fill_factor column in the sys.indexes catalog view.
Important
Creating an index with a FILLFACTOR less than 100 increases the amount of storage space the data occupies because the Database Engine redistributes the data according to the fill factor when it creates or rebuilds an index.
For more information, see Specify fill factor for an index.
SORT_IN_TEMPDB = { ON | OFF }
Specifies whether to store temporary sort results in tempdb. The default is OFF except for Azure SQL Database Hyperscale. For all index build operations in Hyperscale, SORT_IN_TEMPDB is always ON unless a resumable index build is used. For resumable index builds, SORT_IN_TEMPDB is always OFF.
ON
The intermediate sort results that are used to build the index are stored in
tempdb. This might reduce the time required to create an index. However, this increases the amount of disk space that is used during the index build.OFF
The intermediate sort results are stored in the same database as the index.
In addition to the space required in the user database to create the index, tempdb must have about the same amount of additional space to hold the intermediate sort results. For more information, see SORT_IN_TEMPDB option for indexes.
In backward compatible syntax, WITH SORT_IN_TEMPDB is equivalent to WITH SORT_IN_TEMPDB = ON.
IGNORE_DUP_KEY = { ON | OFF }
Specifies the error response when an insert operation attempts to insert duplicate key values into a unique index. The IGNORE_DUP_KEY option applies only to insert operations after the index is created or rebuilt. The option has no effect when executing CREATE INDEX, ALTER INDEX, or UPDATE. The default is OFF.
ON
A warning message occurs when duplicate key values are inserted into a unique index. Only the rows violating the uniqueness constraint aren't inserted.
OFF
An error message occurs when duplicate key values are inserted into a unique index. The entire
INSERTstatement is rolled back.
IGNORE_DUP_KEY can't be set to ON for indexes created on a view, non-unique indexes, XML indexes, spatial indexes, and filtered indexes.
To view the IGNORE_DUP_KEY setting for an index, use the ignore_dup_key column in the sys.indexes catalog view.
In backward compatible syntax, WITH IGNORE_DUP_KEY is equivalent to WITH IGNORE_DUP_KEY = ON.
STATISTICS_NORECOMPUTE = { ON | OFF}
Specifies whether statistics are recomputed. The default is OFF.
ON
Out-of-date statistics are not automatically recomputed.
OFF
Automatic statistics updating are enabled.
To restore automatic statistics updating, set the STATISTICS_NORECOMPUTE to OFF, or execute UPDATE STATISTICS without the NORECOMPUTE clause.
Warning
If you disable automatic recomputation of statistics by setting STATISTICS_NORECOMPUTE = ON, you might prevent the query optimizer from picking optimal execution plans for queries involving the table.
Setting STATISTICS_NORECOMPUTE to ON doesn't prevent the update of index statistics that occurs during the index rebuild operation.
In backward compatible syntax, WITH STATISTICS_NORECOMPUTE is equivalent to WITH STATISTICS_NORECOMPUTE = ON.
STATISTICS_INCREMENTAL = { ON | OFF }
Applies to: SQL Server 2014 (12.x) and later versions, Azure SQL Database, SQL database in Microsoft Fabric, and Azure SQL Managed Instance
When ON, the statistics created are per partition statistics. When OFF, the statistics tree is dropped and SQL Server re-computes the statistics. The default is OFF.
If per partition statistics are not supported the option is ignored and a warning is generated. Incremental statistics are not supported in the following cases:
- Statistics created with indexes that are not partition-aligned with the base table.
- Statistics created on Always On readable secondary databases.
- Statistics created on read-only databases.
- Statistics created on filtered indexes.
- Statistics created on views.
- Statistics created on internal tables.
- Statistics created with spatial indexes or XML indexes.
DROP_EXISTING = { ON | OFF }
Is an option to drop and rebuild the existing clustered or nonclustered index with modified column specifications, and keep the same name for the index. The default is OFF.
ON
Specifies to drop and rebuild the existing index, which must have the same name as the parameter index_name.
OFF
Specifies not to drop and rebuild the existing index. SQL Server displays an error if the specified index name already exists.
With DROP_EXISTING, you can change:
- A nonclustered rowstore index to a clustered rowstore index.
With DROP_EXISTING, you can't change:
- A clustered rowstore index to a nonclustered rowstore index.
- A clustered columnstore index to any type of rowstore index.
In backward compatible syntax, WITH DROP_EXISTING is equivalent to WITH DROP_EXISTING = ON.
ONLINE = { ON | OFF }
Specifies whether underlying tables and associated indexes are available for queries and data modification during the index operation. The default is OFF.
Important
Online index operations are not available in every edition of SQL Server. For a list of features supported by the editions in SQL Server, see Editions and supported features of SQL Server 2025.
ON
Long-term table locks are not held for the duration of the index operation. During the main phase of the index operation, only an intent shared (
IS) lock is held on the source table. This enables queries or updates to the underlying table and indexes to proceed. At the start of the operation, a shared (S) lock is held on the source object for a short period of time. At the end of the operation, for a short period of time, a shared (S) lock is acquired on the object if a nonclustered index is being created. A schema modification (Sch-M) lock is acquired when a clustered index is created or dropped online and when a clustered or nonclustered index is being rebuilt.ONLINEcan't be set toONwhen an index is being created on a local temporary table.Note
You can use the
WAIT_AT_LOW_PRIORITYoption to reduce or avoid blocking during online index operations. For more information, see WAIT_AT_LOW_PRIORITY with online index operations.OFF
Table locks are applied for the duration of the index operation. An offline index operation that creates, rebuilds, or drops a clustered, spatial, or XML index, or rebuilds or drops a nonclustered index, acquires a schema modification (
Sch-M) lock on the table. This prevents all user access to the underlying table for the duration of the operation. An offline index operation that creates a nonclustered index initially acquires a shared (S) lock on the table. This prevents modifications of the underlying table definition, but allows reading and modifying the data in the table while the index build is in progress.
For more information, see Perform index operations online and Guidelines for online index operations.
Indexes, including indexes on global temp tables, can be created online except for the following cases:
- XML index
- Index on a local temp table
- Initial unique clustered index on a view
- Disabled clustered indexes
- Clustered columnstore indexes in SQL Server 2017 (14.x)) and older versions
- Nonclustered columnstore indexes in SQL Server 2016 (13.x)) and older versions
- Clustered index, if the underlying table contains LOB data types (image, ntext, text) and spatial data types
- varchar(max) and varbinary(max) columns can't be part of an index key. In SQL Server (starting with SQL Server 2012 (11.x)), in Azure SQL Database, SQL database in Microsoft Fabric, and in Azure SQL Managed Instance, when a table contains varchar(max) or varbinary(max) columns, a clustered index containing other columns can be built or rebuilt using the
ONLINEoption. - Nonclustered indexes on a table with a clustered columnstore index
For more information, see How online index operations work.
RESUMABLE = { ON | OFF }
Applies to: SQL Server 2019 (15.x) and later versions, Azure SQL Database, SQL database in Microsoft Fabric, and Azure SQL Managed Instance
Specifies whether an online index operation is resumable. For more information, see Resumable index operations and Resumable index considerations.
ON
Index operation is resumable.
OFF
Index operation isn't resumable.
MAX_DURATION = time [MINUTES] used with RESUMABLE = ON (requires ONLINE = ON)
Applies to: SQL Server 2019 (15.x) and later versions, Azure SQL Database, SQL database in Microsoft Fabric, and Azure SQL Managed Instance
Specifies for how long, in minutes, a resumable index operation is executed before it's paused.
ALLOW_ROW_LOCKS = { ON | OFF }
Specifies whether row locks are allowed. The default is ON.
ON
Row locks are allowed when accessing the index. The Database Engine determines when row locks are used.
OFF
Row locks are not used.
ALLOW_PAGE_LOCKS = { ON | OFF }
Specifies whether page locks are allowed. The default is ON.
ON
Page locks are allowed when accessing the index. The Database Engine determines when page locks are used.
OFF
Page locks are not used.
OPTIMIZE_FOR_SEQUENTIAL_KEY = { ON | OFF }
Applies to: SQL Server 2019 (15.x) and later versions, Azure SQL Database, SQL database in Microsoft Fabric, and Azure SQL Managed Instance
Specifies whether or not to optimize to avoid last-page insert contention. The default is OFF. See the Sequential keys section for more information.
MAXDOP = max_degree_of_parallelism
Overrides the max degree of parallelism configuration option for the index operation. For more information, see Configure the max degree of parallelism Server Configuration Option. Use MAXDOP to limit the degree of parallelism and the resulting resource consumption for an index build operation.
max_degree_of_parallelism can be:
1
Suppresses parallel plan generation.
>1
Restricts the maximum degree of parallelism used in a parallel index operation to the specified number or less based on the current system workload.
0 (default)
Uses the degree of parallelism specified at the server, database, or workload group level, unless reduced based on the current system workload.
For more information, see Configure parallel index operations.
Note
Parallel index operations are not available in every edition of SQL Server. For a list of features supported by the editions in SQL Server, see Editions and supported features of SQL Server 2025.
DATA_COMPRESSION
Specifies the data compression option for the specified index, partition number, or range of partitions. The options are as follows:
NONE
Index or specified partitions aren't compressed. This doesn't apply to columnstore indexes.
ROW
Index or specified partitions are compressed by using row compression. This doesn't apply to columnstore indexes.
PAGE
Index or specified partitions are compressed by using page compression. This doesn't apply to columnstore indexes.
COLUMNSTORE
Applies to: SQL Server 2014 (12.x) and later versions, Azure SQL Database, SQL database in Microsoft Fabric, and Azure SQL Managed Instance
Applies only to columnstore indexes, including both nonclustered columnstore and clustered columnstore indexes.
COLUMNSTORE_ARCHIVE
Applies to: SQL Server 2014 (12.x) and later versions, Azure SQL Database, SQL database in Microsoft Fabric, and Azure SQL Managed Instance
Applies only to columnstore indexes, including both nonclustered columnstore and clustered columnstore indexes.
COLUMNSTORE_ARCHIVEfurther compresses the specified partition to a smaller size. This can be used for archival, or for other situations that require a smaller storage size and can afford more time for storage and retrieval.
For more information about compression, see Data compression.
XML_COMPRESSION
Applies to: SQL Server 2022 (16.x) and later versions, Azure SQL Database, SQL database in Microsoft Fabric, and Azure SQL Managed Instance
Specifies the XML compression option for the specified index that contains one or more xml data type columns. The options are as follows:
ON
Index or specified partitions are compressed by using XML compression.
OFF
Index or specified partitions are not compressed using XML compression.
ON PARTITIONS ( { | } [ ,...n ] )
Specifies the partitions to which the DATA_COMPRESSION or XML_COMPRESSION settings apply. If the index isn't partitioned, the ON PARTITIONS argument generates an error. If the ON PARTITIONS clause isn't provided, the DATA_COMPRESSION or XML_COMPRESSION option applies to all partitions of a partitioned index.
- Provide the number for a partition, for example:
ON PARTITIONS (2). - Provide the partition numbers for several individual partitions separated by commas, for example:
ON PARTITIONS (1, 5). - Provide both ranges and individual partitions, for example:
ON PARTITIONS (2, 4, 6 TO 8).
TO, for example: ON PARTITIONS (6 TO 8).
To set different types of data compression for different partitions, specify the DATA_COMPRESSION option more than once, for example:
REBUILD WITH
(
DATA_COMPRESSION = NONE ON PARTITIONS (1),
DATA_COMPRESSION = ROW ON PARTITIONS (2, 4, 6 TO 8),
DATA_COMPRESSION = PAGE ON PARTITIONS (3, 5)
);
You can also specify the XML_COMPRESSION option more than once, for example:
REBUILD WITH
(
XML_COMPRESSION = OFF ON PARTITIONS (1),
XML_COMPRESSION = ON ON PARTITIONS (2, 4, 6 TO 8),
XML_COMPRESSION = OFF ON PARTITIONS (3, 5)
);
Remarks
When creating the query plan for the CREATE INDEX statement, the query optimizer might choose to scan another index instead of performing a table scan. The sort operation might be eliminated in some situations. On multiprocessor computers, CREATE INDEX can use parallelism for the scan and sort operations associated with creating the index, in the same way that other queries do. For more information, see Configure parallel index operations.
The CREATE INDEX operation might be minimally logged if the database recovery model is set to either bulk-logged or simple.
Indexes can be created on a temporary table. When the table is dropped or goes out of scope, the indexes are dropped.
A clustered index is built on a table variable when a primary key constraint is added. Similarly, a nonclustered index is built on a table variable when a unique constraint is added. When the table variable goes out of scope, the indexes are dropped.
Indexes support extended properties.
CREATE INDEX is not supported in Microsoft Fabric.
Clustered indexes
Creating a clustered index on a table (heap) or dropping and re-creating an existing clustered index requires additional workspace to be available in the database to accommodate data sorting and a temporary copy of the original table or existing clustered index data. For more information about clustered indexes, see Create clustered indexes and the SQL Server index architecture and design guide.
Nonclustered indexes
Starting with SQL Server 2016 (13.x), in Azure SQL Database, SQL database in Microsoft Fabric, and in Azure SQL Managed Instance, you can create a nonclustered index on a table stored as a clustered columnstore index. If you first create a nonclustered index on a table stored as a heap or clustered index, the index persists if you later convert the table to a clustered columnstore index. It is also not necessary to drop the nonclustered index when you rebuild the clustered columnstore index.
The FILESTREAM_ON option isn't valid when you create a nonclustered index on a table stored as a clustered columnstore index.
Unique indexes
When a unique index exists, the Database Engine checks for duplicate values each time data is added or modified. Operations that would generate duplicate key values are rolled back, and the Database Engine returns an error message. This is true even if the data addition or modification operation changes many rows but causes only one duplicate. If an attempt is made to insert rows when there is a unique index with the IGNORE_DUP_KEY option set to ON, the rows violating the unique index are ignored.
Partitioned indexes
Partitioned indexes are created and maintained in a similar manner to partitioned tables, but like ordinary indexes, they are handled as separate database objects. You can have a partitioned index on a table that isn't partitioned, and you can have a nonpartitioned index on a table that is partitioned.
If you are creating an index on a partitioned table, and don't specify a filegroup on which to place the index, the index is partitioned in the same manner as the underlying table. This is because indexes, by default, are placed on the same filegroups as their underlying tables, and for a partitioned table in the same partition scheme that uses the same partitioning columns. When the index uses the same partition scheme and partitioning column as the table, the index is aligned with the table.
Warning
Creating and rebuilding nonaligned indexes on a table with more than 1,000 partitions is possible, but is not supported. Doing so may cause degraded performance or excessive memory consumption during these operations. We recommend only using aligned indexes when the number of partitions exceeds 1,000.
When partitioning a non-unique, clustered index, the Database Engine by default adds any partitioning columns to the list of clustered index keys, if not already specified.
Indexed views can be created on partitioned tables in the same manner as indexes on tables. For more information about partitioned indexes, see Partitioned tables and indexes and the SQL Server index architecture and design guide.
When an index is created or rebuilt, the query optimizes updates statistics on the index. For a partitioned index, the query optimizer uses the default sampling algorithm instead of scanning all the rows in the table for a nonpartitioned index. To obtain statistics on partitioned indexes by scanning all the rows in the table, use CREATE STATISTICS or UPDATE STATISTICS with the FULLSCAN clause.
Filtered indexes
A filtered index is an optimized nonclustered index, suited for queries that select a small percentage of rows from a table. It uses a filter predicate to index a portion of the data in the table. A well-designed filtered index can improve query performance, reduce storage costs, and reduce maintenance costs.
Required SET options for filtered indexes
The SET options in the Required value column are required whenever any of the following conditions occur:
You create a filtered index.
An
INSERT,UPDATE,DELETE, orMERGEstatement modifies data in a filtered index.The filtered index is used by the query optimizer to produce the query plan.
SEToptionRequired value Default server value Default OLE DB and ODBC value Default DB-Library value ANSI_NULLSONONONOFFANSI_PADDINGONONONOFFANSI_WARNINGS1ONONONOFFARITHABORTONONOFFOFFCONCAT_NULL_YIELDS_NULLONONONOFFNUMERIC_ROUNDABORTOFFOFFOFFOFFQUOTED_IDENTIFIERONONONOFF1 Setting
ANSI_WARNINGStoONimplicitly setsARITHABORTtoONwhen the database compatibility level is set to 90 or higher. If the database compatibility level is set to 80 or earlier, theARITHABORToption must explicitly be set toON.
If the SET options are incorrect, the following conditions can occur:
- Creating the filtered index fails.
- The Database Engine generates an error and rolls back the
INSERT,UPDATE,DELETE, orMERGEstatement that changes data in the index. - Query optimizer doesn't consider the index in the execution plan for any Transact-SQL statements.
For more information about filtered indexes, see Create filtered indexes and the SQL Server index architecture and design guide.
Spatial indexes
For information about spatial indexes, see CREATE SPATIAL INDEX and Spatial indexes overview.
XML indexes
For information about XML indexes see, CREATE XML INDEX and XML Indexes (SQL Server).
Index key size
The maximum size for an index key is 900 bytes for a clustered index and 1,700 bytes for a nonclustered index. (Before SQL Database and SQL Server 2016 (13.x) the limit was always 900 bytes.) Indexes on varchar columns that exceed the byte limit can be created if the existing data in the columns don't exceed the limit at the time the index is created; however, subsequent insert or update operations on the columns that cause the total size to be greater than the limit fail. The index key of a clustered index can't contain varchar columns that have existing data in the ROW_OVERFLOW_DATA allocation unit. If a clustered index is created on a varchar column and the existing data is in the IN_ROW_DATA allocation unit, subsequent insert or update operations on the column that would push the data off-row fail.
Nonclustered indexes can include non-key (included) columns in the leaf level of the index. These columns are not considered by the Database Engine when calculating the index key size. For more information, see Create indexes with included columns and the SQL Server index architecture and design guide.
Note
When tables are partitioned, if the partitioning key columns are not already present in a non-unique clustered index, they are added to the index by the Database Engine. The combined size of the indexed columns (not counting included columns), plus any added partitioning columns cannot exceed 1800 bytes in a non-unique clustered index.
Computed columns
Indexes can be created on computed columns. In addition, computed columns can have the property PERSISTED. This means that the Database Engine stores the computed values in the table, and updates them when any other columns on which the computed column depends are updated. The Database Engine uses these persisted values when it creates an index on the column, and when the index is referenced in a query.
To index a computed column, the computed column must be deterministic and precise. However, using the PERSISTED property expands the type of indexable computed columns to include:
- Computed columns based on Transact-SQL and CLR functions and CLR user-defined type methods that are marked deterministic by the user.
- Computed columns based on expressions that are deterministic as defined by the Database Engine but imprecise.
Persisted computed columns require the following SET options to be set as shown in the previous section Required SET options for filtered indexes.
The UNIQUE or PRIMARY KEY constraint can contain a computed column as long as it satisfies all conditions for indexing. Specifically, the computed column must be deterministic and precise or deterministic and persisted. For more information about determinism, see Deterministic and Nondeterministic Functions.
Computed columns derived from image, ntext, text, varchar(max), nvarchar(max), varbinary(max), and xml data types can be indexed either as a key or included non-key column as long as the computed column data type is allowable as an index key column or non-key column. For example, you can't create a primary XML index on a computed xml column. If the index key size exceeds 900 bytes, a warning message is displayed.
Creating an index on a computed column might cause the failure of an insert or update operation that previously worked. Such a failure might occur when the computed column results in an arithmetic error.
For example, in the following table, although the expression of the computed column c appears to result in an arithmetic error when the row is inserted, the INSERT statement works.
CREATE TABLE t1 (a INT, b INT, c AS a/b);
INSERT INTO t1 VALUES (1, 0);
However, if you create an index on computed column c, the same INSERT statement fails.
CREATE TABLE t1 (a INT, b INT, c AS a/b);
CREATE UNIQUE CLUSTERED INDEX Idx1 ON t1(c);
INSERT INTO t1 VALUES (1, 0);
For more information, see Indexes on computed columns.
Included columns in indexes
Non-key columns, called included columns, can be added to the leaf level of a nonclustered index to improve query performance by covering the query. That is, all columns referenced in the query are included in the index as either key or non-key columns. This allows the query optimizer to obtain all required information from a nonclustered index scan or seek; the table or clustered index data isn't accessed. For more information, see Create indexes with included columns and the SQL Server index architecture and design guide.
Specifying index options
SQL Server 2005 (9.x) introduced new index options and also modified the way in which options are specified. In the backward compatible syntax, WITH option_name is equivalent to WITH (option_name = ON). When you set index options, the following rules apply:
- New index options can only be specified by using
WITH (.= ) - Options can't be specified by using both the backward compatible and new syntax in the same statement. For example, specifying
WITH (DROP_EXISTING, ONLINE = ON)causes the statement to fail. - When you create an XML index, the options must be specified by using
WITH (.= )
DROP_EXISTING clause
You can use the DROP_EXISTING clause to rebuild the index, add or drop columns, modify options, modify column sort order, or change the partition scheme or filegroup.
If the index enforces a PRIMARY KEY or UNIQUE constraint and the index definition isn't altered in any way, the index is dropped and re-created preserving the existing constraint. However, if the index definition is altered the statement fails. To change the definition of a PRIMARY KEY or UNIQUE constraint, drop the constraint and add a constraint with the new definition.
DROP_EXISTING enhances performance when you re-create a clustered index, with either the same or different set of keys, on a table that also has nonclustered indexes. DROP_EXISTING replaces the execution of a DROP INDEX statement on the old clustered index followed by the execution of a CREATE INDEX statement for the new clustered index. The nonclustered indexes are rebuilt once, and then only if the index definition has changed. The DROP_EXISTING clause doesn't rebuild the nonclustered indexes when the index definition has the same index name, key and partition columns, uniqueness attribute, and sort order as the original index.
Whether the nonclustered indexes are rebuilt or not, they always remain in their original filegroups or partition schemes and use the original partition functions. If a clustered index is rebuilt to a different filegroup or partition scheme, the nonclustered indexes are not moved to coincide with the new location of the clustered index. Therefore, even if the nonclustered indexes previously aligned with the clustered index, they might no longer be aligned with it. For more information about partitioned index alignment, see Partitioned tables and indexes.
The DROP_EXISTING clause doesn't sort the data again if the same index key columns are used in the same order and with the same ascending or descending order, unless the index statement specifies a nonclustered index and the ONLINE option is set to OFF. If the clustered index is disabled, the CREATE INDEX WITH DROP_EXISTING operation must be performed with ONLINE set to OFF. If a nonclustered index is disabled and isn't associated with a disabled clustered index, the CREATE INDEX WITH DROP_EXISTING operation can be performed with ONLINE set to OFF or ON.
Note
When indexes with 128 extents or more are dropped or rebuilt, the Database Engine defers the actual page deallocations, and their associated locks, until after the transaction commits. For more information, see Deferred deallocation.
ONLINE option
The following guidelines apply for performing index operations online:
- The underlying table can't be altered, truncated, or dropped while an online index operation is in process.
- Additional temporary disk space is required during the index operation.
- Online operations can be performed on partitioned indexes and indexes that contain persisted computed columns, or included columns.
- The
WAIT_AT_LOW_PRIORITYargument option allows you to decide how the index operation proceeds when it waits for aSch-Mlock. For more information, see WAIT_AT_LOW_PRIORITY
For more information, see Perform index operations online.
Resumable index operations
Applies to: SQL Server 2019 (15.x) and later versions, Azure SQL Database, SQL database in Microsoft Fabric, and Azure SQL Managed Instance
You can make an online index create operation resumable. That means that the index build can be stopped and later restarted from the point where it stopped. To run an index build as resumable, specify the RESUMABLE = ON option.
The following guidelines apply to resumable index operations:
- To use the
RESUMABLEoption you must also use theONLINEoption. - The
RESUMABLEoption isn't persisted in the metadata for a given index and applies only to the duration of the current DDL statement. Therefore, theRESUMABLE = ONclause must be specified explicitly to enable resumability. - The
MAX_DURATIONoption can be specified in two contexts:MAX_DURATIONfor theRESUMABLEoption specifies the time interval for an index being rebuilt. After this time elapses, and if the index rebuild is still running, it is paused. You decide when the rebuild for a paused index can be resumed. The time in minutes forMAX_DURATIONmust be greater than 0 minutes and less than or equal to one week (7 * 24 * 60 = 10080 minutes). A long pause in an index operation might noticeably affect the DML performance on a specific table as well as the database disk capacity since both the original index and the newly created index require disk space and need to be updated by DML operations. IfMAX_DURATIONoption is omitted, the index operation continues until completion or until a failure occurs.MAX_DURATIONfor theWAIT_AT_LOW_PRIORITYoption specifies the time to wait using low priority locks if the index operation is blocked, before taking action. For more information, see WAIT_AT_LOW_PRIORITY with online index operations.
- To pause the index operation immediately, you can execute the
ALTER INDEX PAUSEcommand, or execute theKILLcommand. - Re-executing the original
CREATE INDEXstatement with the same parameters resumes a paused index build operation. You can also resume a paused index build operation by executing theALTER INDEX RESUMEstatement. - The
ABORTcommand kills the session that is running an index build and cancels the index operation. You cannot resume an index operation that has been aborted.
A resumable index operation runs until it completes, pauses, or fails. In case the operation pauses, an error is issued indicating that the operation was paused and that the index creation did not complete. In case the operation fails, an error is issued as well.
To see if an index operation is executed as a resumable operation and to check its current execution state, use the sys.index_resumable_operations catalog view.
Resources
The following resources are required for resumable index operations:
- Additional space required to keep the index being built, including the time when build is paused.
- Additional log throughput during the sorting phase. The overall log space usage for resumable index is less compared to regular online index create and allows log truncation during this operation.
- DDL statements attempting to modify the table associated with the index being created while the index operation is paused aren't allowed.
- Ghost cleanup is blocked on the in-build index for the duration of the operation both while paused and while the operation is running.
- If the table contains LOB columns, a resumable clustered index build requires a schema modification (
Sch-M) lock at the start of the operation.
Current functional limitations
Resumable index create operations have the following limitations:
- After a resumable online index create operation is paused, the initial value of
MAXDOPcan't be changed. - The
SORT_IN_TEMPDB = ONoption isn't supported for resumable index operations. - The DDL command with
RESUMABLE = ONcan't be executed inside an explicit transaction. - You cannot create an index using a resumable index operation if the index contains:
- A computed or
timestamp(rowversion) column as a key column. - A computed or LOB column as an included column.
- A computed or
- Resumable index operations aren't supported for:
- The
ALTER INDEX REBUILD ALLcommand - The
ALTER TABLE REBUILDcommand - Columnstore indexes
- Filtered indexes
- Disabled indexes
- The
WAIT_AT_LOW_PRIORITY with online index operations
Applies to: SQL Server 2022 (16.x) and later versions, Azure SQL Database, SQL database in Microsoft Fabric, and Azure SQL Managed Instance
When you don't use the WAIT_AT_LOW_PRIORITY option, all active blocking transactions holding locks on the table or index must complete for the index create operation to start and to complete. When the online index operation starts and before it completes, it needs to acquire a shared (S) or a schema modification (Sch-M) lock on the table and hold it for a short time. Even though the lock is held for a short time only, it might significantly affect workload throughput, increase query latency, or cause execution timeouts.
To avoid these problems, the WAIT_AT_LOW_PRIORITY option allows you to manage the behavior of S or Sch-M locks required for an online index operation to start and complete, selecting from three options. In all cases, if during the wait time specified by MAX_DURATION = n [minutes] there is no blocking that involves the index operation, the index operation proceeds immediately.
WAIT_AT_LOW_PRIORITY makes the online index operation wait using low priority locks, allowing other operations using normal priority locks to proceed in the meantime. Omitting the WAIT_AT_LOW_PRIORITY option is equivalent to WAIT_AT_LOW_PRIORITY (MAX_DURATION = 0 minutes, ABORT_AFTER_WAIT = NONE).
MAX_DURATION = time [MINUTES]
The wait time (an integer value specified in minutes) that the online index operation waits using low priority locks. If the operation is blocked for the MAX_DURATION time, the specified ABORT_AFTER_WAIT action is executed. MAX_DURATION time is always in minutes, and the word MINUTES can be omitted.
ABORT_AFTER_WAIT = [NONE | SELF | BLOCKERS ]
NONE: Continue waiting for the lock with normal priority.SELF: Exit the online index operation currently being executed, without taking any action. The optionSELFcan't be used whenMAX_DURATIONis 0.BLOCKERS: Kill all user transactions that block the online index operation so that the operation can continue. TheBLOCKERSoption requires the principal executing theCREATE INDEXorALTER INDEXstatement to have theALTER ANY CONNECTIONpermission.
You can use the following extended events to monitor index operations that wait for locks at low priority:
lock_request_priority_stateprocess_killed_by_abort_blockersddl_with_wait_at_low_priority
Row and page locks options
When ALLOW_ROW_LOCKS = ON and ALLOW_PAGE_LOCK = ON, row-, page-, and table-level locks are allowed when accessing the index. The Database Engine chooses the appropriate lock and can escalate the lock from a row or page lock to a table lock.
When ALLOW_ROW_LOCKS = OFF and ALLOW_PAGE_LOCK = OFF, only a table-level lock is allowed when accessing the index.
Warning
It is not recommended to disable row or page locks on an index. Concurrency-related problems might occur, and certain functionality might be unavailable. For example, an index can't be reorganized when ALLOW_PAGE_LOCKS is set to OFF.
Sequential keys
Applies to: SQL Server 2019 (15.x) and later versions, in Azure SQL Database, SQL database in Microsoft Fabric, and in Azure SQL Managed Instance.
Last-page insert contention is a common performance problem that occurs when a large number of concurrent threads attempt to insert rows into an index with a sequential key. An index is considered sequential when the leading key column contains values that are always increasing (or decreasing), such as an identity column or a date that defaults to the current date/time. Because the keys being inserted are sequential, all new rows are inserted at the end of the index structure - in other words, on the same page. This leads to contention for the page in memory which can be observed as several threads waiting to acquire a latch for the page in question. The corresponding wait type is PAGELATCH_EX.
Enabling the OPTIMIZE_FOR_SEQUENTIAL_KEY index option enables an optimization within the database engine that helps improve throughput for high-concurrency inserts into the index. It is intended for indexes that have a sequential key and thus are prone to last-page insert contention, but it may also help with indexes that have hot spots in other areas of the B-Tree index structure.
Note
Documentation uses the term B-tree generally in reference to indexes. In rowstore indexes, the Database Engine implements a B+ tree. This does not apply to columnstore indexes or indexes on memory-optimized tables. For more information, see the SQL Server and Azure SQL index architecture and design guide.
Data compression
For more information about data compression, see Data compression.
The following are the key points to consider in the context of index build operations when data compression is used:
- Compression can allow more rows to be stored on a page, but doesn't change the maximum row size.
- Non-leaf pages of an index are not page compressed but can be row compressed.
- Each nonclustered index has an individual compression setting, and doesn't inherit the compression setting of the underlying table.
- When a clustered index is created on a heap, the clustered index inherits the compression state of the heap unless an alternative compression state is specified.
To evaluate how changing the compression state affects the space usage by a table, an index, or a partition, use the sp_estimate_data_compression_savings stored procedure.
XML compression
Applies to: SQL Server 2022 (16.x) and later versions, Azure SQL Database, SQL database in Microsoft Fabric, and Azure SQL Managed Instance.
Many of the data compression considerations apply to XML compression. You should also be aware of the following considerations:
- When a list of partitions is specified, XML compression can be enabled on individual partitions. If the list of partitions isn't specified, all partitions are set to use XML compression. When a table or index is created, XML data compression is disabled unless otherwise specified. When a table is modified, the existing compression is preserved unless otherwise specified.
- If you specify a list of partitions or a partition that is out of range, an error is generated.
- When a clustered index is created on a heap, the clustered index inherits the XML compression state of the heap unless an alternative compression option is specified.
- Changing the XML compression setting of a heap requires all nonclustered indexes on the table to be rebuilt so that they have pointers to the new row locations in the heap.
- You can enable or disable XML compression online or offline. Enabling compression on a heap is single threaded for an online operation.
- To determine the XML compression state of partitions in a partitioned table, use the
xml_compressioncolumn of thesys.partitionscatalog view.
Index statistics
When a rowstore index is created, the Database Engine also creates statistics on the key columns of the index. The name of the statistics object in the sys.stats catalog view matches the name of the index. For a non-partitioned index, the statistics are built using a full scan of the data. For a partitioned index, statistics are build using the default sampling algorithm.
When a columnstore index is created, the Database Engine creates a statistics object in sys.stats as well. This statistics object doesn't contain statistics data such as the histogram and the density vector. It is used when creating a database clone by scripting the database. At that time, the DBCC SHOW_STATISTICS and UPDATE STATISTICS ... WITH STATS_STREAM commands are used to obtain columnstore metadata such as segment, dictionary, and delta store size and add it to the statistics on the columnstore index. This metadata is obtained dynamically at query compilation time for a regular database, but is provided by the statistics object for a database clone. The UPDATE STATISTICS command isn't supported for the statistics object on a columnstore index in any other scenario.
Permissions
Requires the ALTER permission on the table or view or membership in the db_ddladmin fixed database role.
Limitations and restrictions
In Azure Synapse Analytics, you can't create:
- A clustered or nonclustered rowstore index on a data warehouse table when a columnstore index already exists. This behavior is different from SMP SQL Server which allows both rowstore and columnstore indexes to co-exist on the same table.
- You can't create an index on a view.
Metadata
To view information on existing indexes, you can query the sys.indexes catalog view.
Version notes
- Azure SQL Database and SQL database in Microsoft Fabric don't support filegroups other than
PRIMARY. - Azure SQL Database, SQL database in Microsoft Fabric, and Azure SQL Managed Instance don't support
FILESTREAMoptions. - Columnstore indexes aren't available before SQL Server 2012 (11.x).
- Resumable index operations are available starting with SQL Server 2017 (14.x), in Azure SQL Database, SQL database in Microsoft Fabric, and in Azure SQL Managed Instance.
Examples: All versions. Uses the AdventureWorks database
A. Create a simple nonclustered rowstore index
The following examples create a nonclustered index on the VendorID column of the Purchasing.ProductVendor table.
CREATE INDEX IX_VendorID ON ProductVendor (VendorID);
CREATE INDEX IX_VendorID ON dbo.ProductVendor (VendorID DESC, Name ASC, Address DESC);
CREATE INDEX IX_VendorID ON Purchasing..ProductVendor (VendorID);
B. Create a simple nonclustered rowstore composite index
The following example creates a nonclustered composite index on the SalesQuota and SalesYTD columns of the Sales.SalesPerson table.
CREATE NONCLUSTERED INDEX IX_SalesPerson_SalesQuota_SalesYTD ON Sales.SalesPerson (SalesQuota, SalesYTD);
C. Create an index on a table in another database
The following example creates a clustered index on the VendorID column of the ProductVendor table in the Purchasing database.
CREATE CLUSTERED INDEX IX_ProductVendor_VendorID ON Purchasing..ProductVendor (VendorID);
D. Add a column to an index
The following example creates index IX_FF with two columns from the dbo.FactFinance table. The next statement rebuilds the index with one more column and keeps the existing name.
CREATE INDEX IX_FF ON dbo.FactFinance (FinanceKey ASC, DateKey ASC);
-- Rebuild and add the OrganizationKey
CREATE INDEX IX_FF ON dbo.FactFinance (FinanceKey, DateKey, OrganizationKey DESC)
WITH (DROP_EXISTING = ON);
Examples: SQL Server, Azure SQL Database, SQL database in Fabric
E. Create a unique nonclustered index
The following example creates a unique nonclustered index on the Name column of the Production.UnitMeasure table in the AdventureWorks2025 database. The index will enforce uniqueness on the data inserted into the Name column.
CREATE UNIQUE INDEX AK_UnitMeasure_Name
ON Production.UnitMeasure(Name);
The following query tests the uniqueness constraint by attempting to insert a row with the same value as that in an existing row.
-- Verify the existing value.
SELECT Name FROM Production.UnitMeasure WHERE Name = N'Ounces';
GO
INSERT INTO Production.UnitMeasure (UnitMeasureCode, Name, ModifiedDate)
VALUES ('OC', 'Ounces', GETDATE());
The resulting error message is:
Server: Msg 2601, Level 14, State 1, Line 1
Cannot insert duplicate key row in object 'UnitMeasure' with unique index 'AK_UnitMeasure_Name'. The statement has been terminated.
F. Use the IGNORE_DUP_KEY option
The following example demonstrates the effect of the IGNORE_DUP_KEY option by inserting multiple rows into a temporary table first with the option set to ON and again with the option set to OFF. A single row is inserted into the #Test table that will intentionally cause a duplicate value when the second multiple-row INSERT statement is executed. A count of rows in the table returns the number of rows inserted.
CREATE TABLE #Test (C1 NVARCHAR(10), C2 NVARCHAR(50), C3 DATETIME);
GO
CREATE UNIQUE INDEX AK_Index ON #Test (C2)
WITH (IGNORE_DUP_KEY = ON);
GO
INSERT INTO #Test VALUES (N'OC', N'Ounces', GETDATE());
INSERT INTO #Test SELECT * FROM Production.UnitMeasure;
GO
SELECT COUNT(*) AS [Number of rows] FROM #Test;
GO
DROP TABLE #Test;
GO
Here are the results of the second INSERT statement.
Server: Msg 3604, Level 16, State 1, Line 5 Duplicate key was ignored.
Number of rows
--------------
38
Notice that the rows inserted from the Production.UnitMeasure table that did not violate the uniqueness constraint were successfully inserted. A warning was issued and the duplicate row ignored, but the entire transaction was not rolled back.
The same statements are executed again, but with IGNORE_DUP_KEY set to OFF.
CREATE TABLE #Test (C1 NVARCHAR(10), C2 NVARCHAR(50), C3 DATETIME);
GO
CREATE UNIQUE INDEX AK_Index ON #Test (C2)
WITH (IGNORE_DUP_KEY = OFF);
GO
INSERT INTO #Test VALUES (N'OC', N'Ounces', GETDATE());
INSERT INTO #Test SELECT * FROM Production.UnitMeasure;
GO
SELECT COUNT(*) AS [Number of rows] FROM #Test;
GO
DROP TABLE #Test;
GO
Here are the results of the second INSERT statement.
Server: Msg 2601, Level 14, State 1, Line 5
Cannot insert duplicate key row in object '#Test' with unique index
'AK_Index'. The statement has been terminated.
Number of rows
--------------
1
Notice that none of the rows from the Production.UnitMeasure table were inserted into the table even though only one row in the table violated the UNIQUE index constraint.
G. Using DROP_EXISTING to drop and re-create an index
The following example drops and re-creates an existing index on the ProductID column of the Production.WorkOrder table in the AdventureWorks2025 database by using the DROP_EXISTING option. The options FILLFACTOR and PAD_INDEX are also set.
CREATE NONCLUSTERED INDEX IX_WorkOrder_ProductID
ON Production.WorkOrder(ProductID)
WITH (FILLFACTOR = 80,
PAD_INDEX = ON,
DROP_EXISTING = ON);
GO
H. Create an index on a view
The following example creates a view and an index on that view. Two queries are included that use the indexed view.
-- Set the options to support indexed views
SET NUMERIC_ROUNDABORT OFF;
SET ANSI_PADDING, ANSI_WARNINGS, CONCAT_NULL_YIELDS_NULL, ARITHABORT,
QUOTED_IDENTIFIER, ANSI_NULLS ON;
GO
-- Create view with schemabinding
IF OBJECT_ID ('Sales.vOrders', 'view') IS NOT NULL
DROP VIEW Sales.vOrders;
GO
CREATE VIEW Sales.vOrders
WITH SCHEMABINDING
AS
SELECT SUM(UnitPrice * OrderQty * (1.00 - UnitPriceDiscount)) AS Revenue,
OrderDate, ProductID, COUNT_BIG(*) AS COUNT
FROM Sales.SalesOrderDetail AS od, Sales.SalesOrderHeader AS o
WHERE od.SalesOrderID = o.SalesOrderID
GROUP BY OrderDate, ProductID;
GO
-- Create an index on the view
CREATE UNIQUE CLUSTERED INDEX IDX_V1
ON Sales.vOrders (OrderDate, ProductID);
GO
-- This query can use the indexed view even though the view is
-- not specified in the FROM clause.
SELECT SUM(UnitPrice * OrderQty * (1.00 - UnitPriceDiscount)) AS Rev,
OrderDate, ProductID
FROM Sales.SalesOrderDetail AS od
JOIN Sales.SalesOrderHeader AS o ON od.SalesOrderID = o.SalesOrderID
AND ProductID BETWEEN 700 AND 800
AND OrderDate >= CONVERT(DATETIME, '05/01/2002', 101)
GROUP BY OrderDate, ProductID
ORDER BY Rev DESC;
GO
-- This query can use the above indexed view
SELECT OrderDate, SUM(UnitPrice * OrderQty * (1.00 - UnitPriceDiscount)) AS Rev
FROM Sales.SalesOrderDetail AS od
JOIN Sales.SalesOrderHeader AS o ON od.SalesOrderID = o.SalesOrderID
AND DATEPART(mm, OrderDate) = 3
AND DATEPART(yy, OrderDate) = 2002
GROUP BY OrderDate
ORDER BY OrderDate ASC;
GO
I. Create an index with included (non-key) columns
The following example creates a nonclustered index with one key column (PostalCode) and four non-key columns (AddressLine1, AddressLine2, City, StateProvinceID). A query that is covered by the index follows. To display the index that is selected by the query optimizer, on the Query menu in SQL Server Management Studio, select Display Actual Execution Plan before executing the query.
CREATE NONCLUSTERED INDEX IX_Address_PostalCode
ON Person.Address (PostalCode)
INCLUDE (AddressLine1, AddressLine2, City, StateProvinceID);
GO
SELECT AddressLine1, AddressLine2, City, StateProvinceID, PostalCode
FROM Person.Address
WHERE PostalCode BETWEEN N'98000' and N'99999';
GO
J. Create a partitioned index
The following example creates a nonclustered partitioned index on TransactionsPS1, an existing partition scheme in the AdventureWorks2025 database. This example assumes the partitioned index sample has been installed.
CREATE NONCLUSTERED INDEX IX_TransactionHistory_ReferenceOrderID
ON Production.TransactionHistory (ReferenceOrderID)
ON TransactionsPS1 (TransactionDate);
GO
K. Creating a filtered index
The following example creates a filtered index on the Production.BillOfMaterials table in the AdventureWorks2025 database. The filter predicate can include columns that are not key columns in the filtered index. The predicate in this example selects only the rows where EndDate is non-NULL.
CREATE NONCLUSTERED INDEX "FIBillOfMaterialsWithEndDate"
ON Production.BillOfMaterials (ComponentID, StartDate)
WHERE EndDate IS NOT NULL;
L. Create a compressed index
The following example creates an index on a nonpartitioned table by using row compression.
CREATE NONCLUSTERED INDEX IX_INDEX_1
ON T1 (C2)
WITH (DATA_COMPRESSION = ROW);
GO
The following example creates an index on a partitioned table by using row compression on all partitions of the index.
CREATE CLUSTERED INDEX IX_PartTab2Col1
ON PartitionTable1 (Col1)
WITH (DATA_COMPRESSION = ROW);
GO
The following example creates an index on a partitioned table by using page compression on partition 1 of the index and row compression on partitions 2 through 4 of the index.
CREATE CLUSTERED INDEX IX_PartTab2Col1
ON PartitionTable1 (Col1)
WITH (
DATA_COMPRESSION = PAGE ON PARTITIONS(1),
DATA_COMPRESSION = ROW ON PARTITIONS (2 TO 4)
);
GO
M. Create an index with XML compression
Applies to: SQL Server 2022 (16.x) and later versions, Azure SQL Database, SQL database in Microsoft Fabric, and Azure SQL Managed Instance.
The following example creates an index on a nonpartitioned table by using XML compression. At least one column in the index must be the xml data type.
CREATE NONCLUSTERED INDEX IX_INDEX_1
ON T1 (C2)
WITH (XML_COMPRESSION = ON);
GO
The following example creates an index on a partitioned table by using XML compression on all partitions of the index.
CREATE CLUSTERED INDEX IX_PartTab2Col1
ON PartitionTable1 (Col1)
WITH (XML_COMPRESSION = ON);
GO
N. Create, resume, pause, and abort resumable index operations
Applies to: SQL Server 2019 (15.x) and later versions, Azure SQL Database, SQL database in Microsoft Fabric, and Azure SQL Managed Instance
-- Execute a resumable online index create statement with MAXDOP=1
CREATE INDEX test_idx1 ON test_table (col1) WITH (ONLINE = ON, MAXDOP = 1, RESUMABLE = ON);
-- Executing the same command again (see above) after an index operation was paused, resumes automatically the index create operation.
-- Execute a resumable online index creates operation with MAX_DURATION set to 240 minutes. After the time expires, the resumable index create operation is paused.
CREATE INDEX test_idx2 ON test_table (col2) WITH (ONLINE = ON, RESUMABLE = ON, MAX_DURATION = 240);
-- Pause a running resumable online index creation
ALTER INDEX test_idx1 ON test_table PAUSE;
ALTER INDEX test_idx2 ON test_table PAUSE;
-- Resume a paused online index creation
ALTER INDEX test_idx1 ON test_table RESUME;
ALTER INDEX test_idx2 ON test_table RESUME;
-- Abort resumable index create operation which is running or paused
ALTER INDEX test_idx1 ON test_table ABORT;
ALTER INDEX test_idx2 ON test_table ABORT;
O. CREATE INDEX with different low priority lock options
The following examples use the WAIT_AT_LOW_PRIORITY option to specify different strategies for dealing with blocking.
--Kill this session after waiting 5 minutes
CREATE CLUSTERED INDEX idx_1 ON dbo.T2 (a) WITH (ONLINE = ON (WAIT_AT_LOW_PRIORITY (MAX_DURATION = 5 MINUTES, ABORT_AFTER_WAIT = SELF)));
GO
--Kill blocker sessions
CREATE CLUSTERED INDEX idx_1 ON dbo.T2 (a) WITH (ONLINE = ON (WAIT_AT_LOW_PRIORITY (MAX_DURATION = 5 MINUTES, ABORT_AFTER_WAIT = BLOCKERS)));
GO
The following example uses both the RESUMABLE option and specifies two MAX_DURATION values, the first applies to the ABORT_AFTER_WAIT option, the second applies to the RESUMABLE option.
--With resumable option; default locking behavior
CREATE CLUSTERED INDEX idx_1 ON dbo.T2 (a) WITH (ONLINE = ON (WAIT_AT_LOW_PRIORITY (MAX_DURATION = 5 MINUTES, ABORT_AFTER_WAIT = NONE)), RESUMABLE = ON, MAX_DURATION = 240 MINUTES);
Examples: Azure Synapse Analytics
P. Basic syntax
Create, resume, pause, and abort resumable index operations
Applies to: SQL Server 2019 (15.x) and later versions, Azure SQL Database, SQL database in Microsoft Fabric, and Azure SQL Managed Instance
-- Execute a resumable online index create statement with MAXDOP=1
CREATE INDEX test_idx ON test_table WITH (ONLINE = ON, MAXDOP = 1, RESUMABLE = ON);
-- Executing the same command again (see above) after an index operation was paused, resumes automatically the index create operation.
-- Execute a resumable online index creates operation with MAX_DURATION set to 240 minutes. After the time expires, the resumable index create operation is paused.
CREATE INDEX test_idx ON test_table WITH (ONLINE = ON, RESUMABLE = ON, MAX_DURATION = 240);
-- Pause a running resumable online index creation
ALTER INDEX test_idx ON test_table PAUSE;
-- Resume a paused online index creation
ALTER INDEX test_idx ON test_table RESUME;
-- Abort resumable index create operation which is running or paused
ALTER INDEX test_idx ON test_table ABORT;
Q. Create a nonclustered index on a table in the current database
The following example creates a nonclustered index on the VendorID column of the ProductVendor table.
CREATE INDEX IX_ProductVendor_VendorID
ON ProductVendor (VendorID);
R. Create a clustered index on a table in another database
The following example creates a nonclustered index on the VendorID column of the ProductVendor table in the Purchasing database.
CREATE CLUSTERED INDEX IX_ProductVendor_VendorID
ON Purchasing..ProductVendor (VendorID);
S. Create an ordered clustered index on a table
The following example creates an ordered clustered index on the c1 and c2 columns of the T1 table in the MyDB database.
CREATE CLUSTERED COLUMNSTORE INDEX MyOrderedCCI ON MyDB.dbo.T1
ORDER (c1, c2);
T. Convert a CCI to an ordered clustered index on a table
The following example converts the existing clustered columnstore index to an ordered clustered columnstore index called MyOrderedCCI on the c1 and c2 columns of the T2 table in the MyDB database.
CREATE CLUSTERED COLUMNSTORE INDEX MyOrderedCCI ON MyDB.dbo.T2
ORDER (c1, c2)
WITH (DROP_EXISTING = ON);
Related content
- Index architecture and design guide
- Perform index operations online
- Indexes and ALTER TABLE
- ALTER INDEX (Transact-SQL)
- CREATE PARTITION FUNCTION (Transact-SQL)
- CREATE PARTITION SCHEME (Transact-SQL)
- CREATE SPATIAL INDEX (Transact-SQL)
- CREATE STATISTICS (Transact-SQL)
- CREATE TABLE (Transact-SQL)
- CREATE XML INDEX (Transact-SQL)
- Data types (Transact-SQL)
- DBCC SHOW_STATISTICS (Transact-SQL)
- DROP INDEX (Transact-SQL)
- XML indexes (SQL Server)
- sys.indexes (Transact-SQL)
- sys.index_columns (Transact-SQL)
- sys.xml_indexes (Transact-SQL)
- EVENTDATA (Transact-SQL)