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----
-title: ALTER INDEX
-summary: An overview of the usage of ALTER INDEX for the TiDB database.
-aliases: ['/docs/dev/sql-statements/sql-statement-alter-index/']
----
-
-# ALTER INDEX
-
-The `ALTER INDEX` statement is used to modify the visibility of the index to `Visible` or `Invisible`. Invisible indexes are maintained by DML statements, but will not be used by the query optimizer. This is useful in scenarios where you want to double-check before removing an index permanently.
-
-## Synopsis
-
-```ebnf+diagram
-AlterTableStmt ::=
-    'ALTER' IgnoreOptional 'TABLE' TableName ( AlterTableSpecListOpt AlterTablePartitionOpt | 'ANALYZE' 'PARTITION' PartitionNameList ( 'INDEX' IndexNameList )? AnalyzeOptionListOpt )
-
-AlterTableSpec ::=
-    TableOptionList
-|   'SET' 'TIFLASH' 'REPLICA' LengthNum LocationLabelList
-|   'CONVERT' 'TO' CharsetKw ( CharsetName | 'DEFAULT' ) OptCollate
-|   'ADD' ( ColumnKeywordOpt IfNotExists ( ColumnDef ColumnPosition | '(' TableElementList ')' ) | Constraint | 'PARTITION' IfNotExists NoWriteToBinLogAliasOpt ( PartitionDefinitionListOpt | 'PARTITIONS' NUM ) )
-|   ( ( 'CHECK' | 'TRUNCATE' ) 'PARTITION' | ( 'OPTIMIZE' | 'REPAIR' | 'REBUILD' ) 'PARTITION' NoWriteToBinLogAliasOpt ) AllOrPartitionNameList
-|   'COALESCE' 'PARTITION' NoWriteToBinLogAliasOpt NUM
-|   'DROP' ( ColumnKeywordOpt IfExists ColumnName RestrictOrCascadeOpt | 'PRIMARY' 'KEY' |  'PARTITION' IfExists PartitionNameList | ( KeyOrIndex IfExists | 'CHECK' ) Identifier | 'FOREIGN' 'KEY' IfExists Symbol )
-|   'EXCHANGE' 'PARTITION' Identifier 'WITH' 'TABLE' TableName WithValidationOpt
-|   ( 'IMPORT' | 'DISCARD' ) ( 'PARTITION' AllOrPartitionNameList )? 'TABLESPACE'
-|   'REORGANIZE' 'PARTITION' NoWriteToBinLogAliasOpt ReorganizePartitionRuleOpt
-|   'ORDER' 'BY' AlterOrderItem ( ',' AlterOrderItem )*
-|   ( 'DISABLE' | 'ENABLE' ) 'KEYS'
-|   ( 'MODIFY' ColumnKeywordOpt IfExists | 'CHANGE' ColumnKeywordOpt IfExists ColumnName ) ColumnDef ColumnPosition
-|   'ALTER' ( ColumnKeywordOpt ColumnName ( 'SET' 'DEFAULT' ( SignedLiteral | '(' Expression ')' ) | 'DROP' 'DEFAULT' ) | 'CHECK' Identifier EnforcedOrNot | 'INDEX' Identifier IndexInvisible )
-|   'RENAME' ( ( 'COLUMN' | KeyOrIndex ) Identifier 'TO' Identifier | ( 'TO' | '='? | 'AS' ) TableName )
-|   LockClause
-|   AlgorithmClause
-|   'FORCE'
-|   ( 'WITH' | 'WITHOUT' ) 'VALIDATION'
-|   'SECONDARY_LOAD'
-|   'SECONDARY_UNLOAD'
-
-IndexInvisible ::=
-    'VISIBLE'
-|   'INVISIBLE'
-```
-
-## Examples
-
-You can modify the visibility of an index using the `ALTER TABLE ... ALTER INDEX ...` statement.
-
-{{< copyable "sql" >}}
-
-```sql
-CREATE TABLE t1 (c1 INT, UNIQUE(c1));
-ALTER TABLE t1 ALTER INDEX c1 INVISIBLE;
-```
-
-```sql
-Query OK, 0 rows affected (0.02 sec)
-```
-
-{{< copyable "sql" >}}
-
-```sql
-SHOW CREATE TABLE t1;
-```
-
-```sql
-+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
-| Table | Create Table
-                                    |
-+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
-| t1    | CREATE TABLE `t1` (
-  `c1` int(11) DEFAULT NULL,
-  UNIQUE KEY `c1` (`c1`) /*!80000 INVISIBLE */
-) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin |
-+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
-1 row in set (0.00 sec)
-```
-
-The optimizer cannot use the **invisible index** of `c1`.
-
-{{< copyable "sql" >}}
-
-```sql
-EXPLAIN SELECT c1 FROM t1 ORDER BY c1;
-```
-
-```sql
-+-------------------------+----------+-----------+---------------+--------------------------------+
-| id                      | estRows  | task      | access object | operator info                  |
-+-------------------------+----------+-----------+---------------+--------------------------------+
-| Sort_4                  | 10000.00 | root      |               | test.t1.c1:asc                 |
-| └─TableReader_8         | 10000.00 | root      |               | data:TableFullScan_7           |
-|   └─TableFullScan_7     | 10000.00 | cop[tikv] | table:t1      | keep order:false, stats:pseudo |
-+-------------------------+----------+-----------+---------------+--------------------------------+
-3 rows in set (0.00 sec)
-```
-
-By comparison, `c2` is a **visible index** and can be used by the optimizer.
-
-{{< copyable "sql" >}}
-
-```sql
-EXPLAIN SELECT c2 FROM t1 ORDER BY c2;
-```
-
-```sql
-+------------------------+----------+-----------+------------------------+-------------------------------+
-| id                     | estRows  | task      | access object          | operator info                 |
-+------------------------+----------+-----------+------------------------+-------------------------------+
-| IndexReader_13         | 10000.00 | root      |                        | index:IndexFullScan_12        |
-| └─IndexFullScan_12     | 10000.00 | cop[tikv] | table:t1, index:c2(c2) | keep order:true, stats:pseudo |
-+------------------------+----------+-----------+------------------------+-------------------------------+
-2 rows in set (0.00 sec)
-```
-
-Even if you use the `USE INDEX` SQL hint to forcibly use indexes, the optimizer still cannot use invisible indexes; otherwise, an error is returned.
-
-{{< copyable "sql" >}}
-
-```sql
-SELECT * FROM t1 USE INDEX(c1);
-```
-
-```sql
-ERROR 1176 (42000): Key 'c1' doesn't exist in table 't1'
-```
-
-> **Note:**
->
-> "Invisible" here means invisible only to the optimizer. You can still modify or delete invisible indexes.
-
-{{< copyable "sql" >}}
-
-```sql
-ALTER TABLE t1 DROP INDEX c1;
-```
-
-```sql
-Query OK, 0 rows affected (0.02 sec)
-```
-
-## MySQL compatibility
-
-* Invisible indexes in TiDB are modeled on the equivalent feature from MySQL 8.0.
-* Similiar to MySQL, TiDB does not permit `PRIMARY KEY` indexes to be made invisible.
-* MySQL provides an optimizer switch `use_invisible_indexes=on` to make all invisible indexes _visible_ again. This functionality is not available in TiDB.
-
-## See also
-
-* [CREATE TABLE](/sql-statements/sql-statement-create-table.md)
-* [CREATE INDEX](/sql-statements/sql-statement-create-index.md)
-* [ADD INDEX](/sql-statements/sql-statement-add-index.md)
-* [DROP INDEX](/sql-statements/sql-statement-drop-index.md)
-* [RENAME INDEX](/sql-statements/sql-statement-rename-index.md)