ALTER INDEX (Transact-SQL)

index_name

Is the name of the index. Index names must be unique within a table or view but do not have to be unique within a database. Index names must follow the rules of identifiers.

ALL

Specifies all indexes associated with the table or view regardless of the index type. Specifying ALL causes the statement to fail if one or more indexes are in an offline or read-only filegroup or the specified operation is not allowed on one or more index types. The following table lists the index operations and disallowed index types.

Specifying ALL with this operation	Fails if the table has one or more
REBUILD WITH ONLINE = ON	XML index Spatial index Large object data type columns: image, text, ntext, varchar(max), nvarchar(max), varbinary(max), and xml
REBUILD PARTITION = partition_number	Nonpartitioned index, XML index, spatial index, or disabled index
REORGANIZE	Indexes with ALLOW_PAGE_LOCKS set to OFF
REORGANIZE PARTITION = partition_number	Nonpartitioned index, XML index, spatial index, or disabled index
IGNORE_DUP_KEY = ON	Spatial index XML index
ONLINE = ON	Spatial index XML index

If ALL is specified with PARTITION = partition_number, all indexes must be aligned. This means that they are partitioned based on equivalent partition functions. Using ALL with PARTITION causes all index partitions with the same partition_number to be rebuilt or reorganized. For more information about partitioned indexes, see Partitioned Tables and Indexes.

database_name

Is the name of the database.

schema_name

Is the name of the schema to which the table or view belongs.

table_or_view_name

Is the name of the table or view associated with the index. To display a report of the indexes on an object, use the sys.indexes catalog view.

REBUILD [ WITH (<rebuild_index_option> [ ,... n]) ]

Specifies the index will be rebuilt using the same columns, index type, uniqueness attribute, and sort order. This clause is equivalent to DBCC DBREINDEX. REBUILD enables a disabled index. Rebuilding a clustered index does not rebuild associated nonclustered indexes unless the keyword ALL is specified. If index options are not specified, the existing index option values stored in sys.indexes are applied. For any index option whose value is not stored in sys.indexes, the default indicated in the argument definition of the option applies.

When you rebuild an XML index or a spatial index, the options ONLINE = ON and IGNORE_DUP_KEY = ON are not valid.

If ALL is specified and the underlying table is a heap, the rebuild operation has no effect on the table. Any nonclustered indexes associated with the table are rebuilt.

The rebuild operation can be minimally logged if the database recovery model is set to either bulk-logged or simple. For more information, see Choosing a Recovery Model for Index Operations.

Note
When you rebuild a primary XML index, the underlying user table is unavailable for the duration of the index operation.

PARTITION

Specifies that only one partition of an index will be rebuilt or reorganized. PARTITION cannot be specified if index_name is not a partitioned index.

PARTITION = ALL rebuilds all partitions.

partition_number

Is the partition number of a partitioned index that is to be rebuilt or reorganized. partition_number is a constant expression that can reference variables. These include user-defined type variables or functions and user-defined functions, but cannot reference a Transact-SQL statement. partition_number must exist or the statement fails.

WITH (<single_partition_rebuild_index_option>)

SORT_IN_TEMPDB, MAXDOP, and DATA_COMPRESSION are the options that can be specified when you rebuild a single partition (PARTITION = n). XML indexes cannot be specified in a single partition rebuild operation.

Rebuilding a partitioned index cannot be performed online. The entire table is locked during this operation.

DISABLE

Marks the index as disabled and unavailable for use by the Database Engine. Any index can be disabled. The index definition of a disabled index remains in the system catalog with no underlying index data. Disabling a clustered index prevents user access to the underlying table data. To enable an index, use ALTER INDEX REBUILD or CREATE INDEX WITH DROP_EXISTING. For more information, see Disabling Indexes.

REORGANIZE

Specifies the index leaf level will be reorganized. This clause is equivalent to DBCC INDEXDEFRAG. ALTER INDEX REORGANIZE statement is always performed online. This means long-term blocking table locks are not held and queries or updates to the underlying table can continue during the ALTER INDEX REORGANIZE transaction. REORGANIZE cannot be specified for a disabled index or an index with ALLOW_PAGE_LOCKS set to OFF.

WITH ( LOB_COMPACTION = { ON | OFF } )

Specifies that all pages that contain large object (LOB) data are compacted. The LOB data types are image, text, ntext, varchar(max), nvarchar(max), varbinary(max), and xml. Compacting this data can improve disk space use. The default is ON.

ON

All pages that contain large object data are compacted.

Reorganizing a specified clustered index compacts all LOB columns that are contained in the clustered index. Reorganizing a nonclustered index compacts all LOB columns that are nonkey (included) columns in the index. For more information, see Creating Indexes with Included Columns.

When ALL is specified, all indexes that are associated with the specified table or view are reorganized, and all LOB columns that are associated with the clustered index, underlying table, or nonclustered index with included columns are compacted.

OFF

Pages that contain large object data are not compacted.

OFF has no effect on a heap.

The LOB_COMPACTION clause is ignored if LOB columns are not present.

SET ( <set_index option> [ ,... n] )

Specifies index options without rebuilding or reorganizing the index. SET cannot be specified for a disabled index.

PAD_INDEX = { ON | OFF }

Specifies index padding. The default is OFF.

ON

The percentage of free space that is specified by FILLFACTOR is applied to the intermediate-level pages of the index. If FILLFACTOR is not specified at the same time PAD_INDEX is set to ON, the fill factor value stored in sys.indexes is used.

OFF or fillfactor is not specified

The intermediate-level pages are filled to near capacity. This leaves sufficient space for at least one row of the maximum size that the index can have, based on the set of keys on the intermediate pages.

For more information, see CREATE INDEX (Transact-SQL).

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 alteration. fillfactor must be an integer value from 1 to 100. The default is 0.

Note
Fill factor values 0 and 100 are the same in all respects.

An explicit FILLFACTOR setting applies only when the index is first created or rebuilt. The Database Engine does not dynamically keep the specified percentage of empty space in the pages. For more information, see CREATE INDEX (Transact-SQL).

To view the fill factor setting, use sys.indexes.

Important
Creating or altering a clustered index with a FILLFACTOR value affects the amount of storage space the data occupies, because the Database Engine redistributes the data when it creates the clustered index.

SORT_IN_TEMPDB = { ON | OFF }

Specifies whether to store the sort results in tempdb. The default is OFF.

ON

The intermediate sort results that are used to build the index are stored in tempdb. If tempdb is on a different set of disks than the user database, this may reduce the time needed 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.

If a sort operation is not required, or if the sort can be performed in memory, the SORT_IN_TEMPDB option is ignored.

For more information, see tempdb and Index Creation.

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 will occur when duplicate key values are inserted into a unique index. Only the rows violating the uniqueness constraint will fail.

OFF

An error message will occur when duplicate key values are inserted into a unique index. The entire INSERT operation will be rolled back.

IGNORE_DUP_KEY cannot be set to ON   for indexes created on a view, non-unique indexes, XML indexes, spatial indexes, and filtered indexes.

To view IGNORE_DUP_KEY, use sys.indexes.

In backward compatible syntax, WITH IGNORE_DUP_KEY is equivalent to WITH IGNORE_DUP_KEY = ON.

STATISTICS_NORECOMPUTE = { ON | OFF }

Specifies whether distribution 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.

Important
Disabling automatic recomputation of distribution statistics may prevent the query optimizer from picking optimal execution plans for queries that involve the table.

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.

For an XML index or spatial index, only ONLINE = OFF is supported, and if ONLINE is set to ON an error is raised.

Note
Online index operations are available only in SQL Server Enterprise, Developer, and Evaluation editions.

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 Share (IS) lock is held on the source table. This allows queries or updates to the underlying table and indexes to continue. At the start of the operation, a Shared (S) lock is very briefly held on the source object. At the end of the operation, an S lock is very briefly held on the source if a nonclustered index is being created, or an SCH-M (Schema Modification) lock is acquired when a clustered index is created or dropped online, or when a clustered or nonclustered index is being rebuilt. ONLINE cannot be set to ON when an index is being created on a local temporary table.

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 acquires a Shared (S) lock on the table. This prevents updates to the underlying table but allows read operations, such as SELECT statements.

For more information, see How Online Index Operations Work. For more information about locks, see Lock Modes.

Indexes, including indexes on global temp tables, can be rebuilt online with the following exceptions:

• XML indexes

• Indexes on local temp tables

• A subset of a partitioned index (An entire partitioned index can be rebuilt online.)

• Clustered indexes if the underlying table contains LOB data types

• Nonclustered indexes that are defined with LOB data type columns

Nonclustered indexes can be rebuilt online if the table contains LOB data types but none of these columns are used in the index definition as either key or nonkey columns.

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 you access the index. The Database Engine determines when page locks are used.

OFF

Page locks are not used.

Note
An index cannot be reorganized when ALLOW_PAGE_LOCKS is set to OFF.

MAXDOP =max_degree_of_parallelism

Overrides the max degree of parallelism configuration option for the duration of the index operation. For more information, see max degree of parallelism Option. Use MAXDOP to limit the number of processors used in a parallel plan execution. The maximum is 64 processors.

Important
Although the MAXDOP option is syntactically supported for all XML indexes, for a spatial index or a primary XML index, ALTER INDEX currently uses only a single processor.

max_degree_of_parallelism can be:

1

Suppresses parallel plan generation.

>1

Restricts the maximum number of processors used in a parallel index operation to the specified number.

0 (default)

Uses the actual number of processors or fewer based on the current system workload.

For more information, see Configuring Parallel Index Operations.

Note
Parallel index operations are available only in SQL Server Enterprise, Developer, and Evaluation editions.

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 are not compressed.

ROW

Index or specified partitions are compressed by using row compression.

PAGE

Index or specified partitions are compressed by using page compression.

For more information about compression, see Creating Compressed Tables and Indexes.

ON PARTITIONS ( { <partition_number_expression> | <range> } [,...n] )

Specifies the partitions to which the DATA_COMPRESSION setting applies. If the index is not partitioned, the ON PARTITIONS argument will generate an error. If the ON PARTITIONS clause is not provided, the DATA_COMPRESSION option applies to all partitions of a partitioned index.

<partition_number_expression> can be specified in the following ways:

• 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: ON PARTITIONS (2, 4, 6 TO 8).

<range> can be specified as partition numbers separated by the word 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:

Copy

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)
)

ALTER INDEX cannot be used to repartition an index or move it to a different filegroup. This statement cannot be used to modify the index definition, such as adding or deleting columns or changing the column order. Use CREATE INDEX with the DROP_EXISTING clause to perform these operations.

When an option is not explicitly specified, the current setting is applied. For example, if a FILLFACTOR setting is not specified in the REBUILD clause, the fill factor value stored in the system catalog will be used during the rebuild process. To view the current index option settings, use sys.indexes.

Note
The values for ONLINE, MAXDOP, and SORT_IN_TEMPDB are not stored in the system catalog. Unless specified in the index statement, the default value for the option is used.

On multiprocessor computers, just like other queries do, ALTER INDEX REBUILD automatically uses more processors to perform the scan and sort operations that are associated with modifying the index. When you run ALTER INDEX REORGANIZE, with or without LOB_COMPACTION, the max degree of parallelism value is a single threaded operation. For more information, see Configuring Parallel Index Operations.

An index cannot be reorganized or rebuilt if the filegroup in which it is located is offline or set to read-only. When the keyword ALL is specified and one or more indexes are in an offline or read-only filegroup, the statement fails.

Rebuilding Indexes

Rebuilding an index drops and re-creates the index. This removes fragmentation, reclaims disk space by compacting the pages based on the specified or existing fill factor setting, and reorders the index rows in contiguous pages. When ALL is specified, all indexes on the table are dropped and rebuilt in a single transaction. FOREIGN KEY constraints do not have to be dropped in advance. When indexes with 128 extents or more are rebuilt, the Database Engine defers the actual page deallocations, and their associated locks, until after the transaction commits. For more information, see Dropping and Rebuilding Large Objects.

Note
Rebuilding or reorganizing small indexes often does not reduce fragmentation. The pages of small indexes are stored on mixed extents. Mixed extents are shared by up to eight objects, so the fragmentation in a small index might not be reduced after reorganizing or rebuilding it. For more information about mixed extents, see Understanding Pages and Extents.

In earlier versions of SQL Server, you could sometimes rebuild a nonclustered index to correct inconsistencies caused by hardware failures. In SQL Server 2008, you may still be able to repair such inconsistencies between the index and the clustered index by rebuilding a nonclustered index offline. However, you cannot repair nonclustered index inconsistencies by rebuilding the index online, because the online rebuild mechanism will use the existing nonclustered index as the basis for the rebuild and thus persist the inconsistency. Rebuilding the index offline, by contrast, will force a scan of the clustered index (or heap) and so remove the inconsistency. As with earlier versions, we recommend recovering from inconsistencies by restoring the affected data from a backup; however, you may be able to repair the index inconsistencies by rebuilding the nonclustered index offline. For more information, see DBCC CHECKDB (Transact-SQL).

Reorganizing Indexes

Disabling Indexes

Setting Options

Online Index Operations

Spatial Index Restrictions

Data Compression

To execute ALTER INDEX, at a minimum, ALTER permission on the table or view is required.

A. Rebuilding an index

USE AdventureWorks;
GO
ALTER INDEX PK_Employee_EmployeeID ON HumanResources.Employee
REBUILD;
GO

B. Rebuilding all indexes on a table and specifying options

USE AdventureWorks;
GO
ALTER INDEX ALL ON Production.Product
REBUILD WITH (FILLFACTOR = 80, SORT_IN_TEMPDB = ON,
              STATISTICS_NORECOMPUTE = ON);
GO

C. Reorganizing an index with LOB compaction

USE AdventureWorks;
GO
ALTER INDEX PK_ProductPhoto_ProductPhotoID ON Production.ProductPhoto
REORGANIZE ;
GO

D. Setting options on an index

USE AdventureWorks;
GO
ALTER INDEX AK_SalesOrderHeader_SalesOrderNumber ON
    Sales.SalesOrderHeader
SET (
    STATISTICS_NORECOMPUTE = ON,
    IGNORE_DUP_KEY = ON,
    ALLOW_PAGE_LOCKS = ON
    ) ;
GO

E. Disabling an index

USE AdventureWorks;
GO
ALTER INDEX IX_Employee_ManagerID ON HumanResources.Employee
DISABLE ;
GO

F. Disabling constraints

USE AdventureWorks;
GO
ALTER INDEX PK_Department_DepartmentID ON HumanResources.Department
DISABLE ;
GO

G. Enabling constraints

USE AdventureWorks;
GO
ALTER INDEX PK_Department_DepartmentID ON HumanResources.Department
REBUILD ;
GO

ALTER TABLE HumanResources.EmployeeDepartmentHistory
CHECK CONSTRAINT FK_EmployeeDepartmentHistory_Department_DepartmentID;
GO

H. Rebuilding a partitioned index

USE AdventureWorks;
GO
-- Verify the partitioned indexes.
SELECT *
FROM sys.dm_db_index_physical_stats (DB_ID(),OBJECT_ID(N'Production.TransactionHistory'), NULL , NULL, NULL);
GO
--Rebuild only partition 5.
ALTER INDEX IX_TransactionHistory_TransactionDate
ON Production.TransactionHistory
REBUILD Partition = 5;
GO

I. Changing the compression setting of an index

ALTER INDEX IX_INDEX1 
ON T1
REBUILD 
WITH ( DATA_COMPRESSION = PAGE )
GO

Reference

Concepts