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ADD INDEX | TiDB SQL Statement Reference
An overview of the usage of ADD INDEX for the TiDB database.
/docs/dev/sql-statements/sql-statement-add-index/
/docs/dev/reference/sql/statements/add-index/

ADD INDEX

The ALTER TABLE.. ADD INDEX statement adds an index to an existing table. This operation is online in TiDB, which means that neither reads or writes to the table are blocked by adding an index.

Warning:

  • DO NOT upgrade a TiDB cluster when a DDL statement is being executed in the cluster (usually for the time-consuming DDL statements such as ADD INDEX and the column type changes).
  • Before the upgrade, it is recommended to use the ADMIN SHOW DDL command to check whether the TiDB cluster has an ongoing DDL job. If the cluster has a DDL job, to upgrade the cluster, wait until the DDL execution is finished or use the ADMIN CANCEL DDL command to cancel the DDL job before you upgrade the cluster.
  • In addition, during the cluster upgrade, DO NOT execute any DDL statement. Otherwise, the issue of undefined behavior might occur.

When you upgrade TiDB from v7.1.0 to a later version, you can ignore the preceding limitations. For details, see the limitations of TiDB smooth upgrade.

Synopsis

AlterTableStmt
         ::= 'ALTER' 'IGNORE'? 'TABLE' TableName AddIndexSpec ( ',' AddIndexSpec )*

AddIndexSpec
         ::= 'ADD' ( ( 'PRIMARY' 'KEY' | ( 'KEY' | 'INDEX' ) 'IF NOT EXISTS'? | 'UNIQUE' ( 'KEY' | 'INDEX' )? ) ( ( Identifier? 'USING' | Identifier 'TYPE' ) IndexType )? | 'FULLTEXT' ( 'KEY' | 'INDEX' )? IndexName ) '(' IndexPartSpecification ( ',' IndexPartSpecification )* ')' IndexOption*

IndexPartSpecification
         ::= ( ColumnName ( '(' LengthNum ')' )? | '(' Expression ')' ) ( 'ASC' | 'DESC' )

IndexOption
         ::= 'KEY_BLOCK_SIZE' '='? LengthNum
           | IndexType
           | 'WITH' 'PARSER' Identifier
           | 'COMMENT' stringLit
           | 'VISIBLE'
           | 'INVISIBLE'

IndexType
         ::= 'BTREE'
           | 'HASH'
           | 'RTREE'

Examples

mysql> CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, c1 INT NOT NULL);
Query OK, 0 rows affected (0.11 sec)

mysql> INSERT INTO t1 (c1) VALUES (1),(2),(3),(4),(5);
Query OK, 5 rows affected (0.03 sec)
Records: 5  Duplicates: 0  Warnings: 0

mysql> EXPLAIN SELECT * FROM t1 WHERE c1 = 3;
+-------------------------+----------+-----------+---------------+--------------------------------+
| id                      | estRows  | task      | access object | operator info                  |
+-------------------------+----------+-----------+---------------+--------------------------------+
| TableReader_7           | 10.00    | root      |               | data:Selection_6               |
| └─Selection_6           | 10.00    | cop[tikv] |               | eq(test.t1.c1, 3)              |
|   └─TableFullScan_5     | 10000.00 | cop[tikv] | table:t1      | keep order:false, stats:pseudo |
+-------------------------+----------+-----------+---------------+--------------------------------+
3 rows in set (0.00 sec)

mysql> ALTER TABLE t1 ADD INDEX (c1);
Query OK, 0 rows affected (0.30 sec)

mysql> EXPLAIN SELECT * FROM t1 WHERE c1 = 3;
+------------------------+---------+-----------+------------------------+---------------------------------------------+
| id                     | estRows | task      | access object          | operator info                               |
+------------------------+---------+-----------+------------------------+---------------------------------------------+
| IndexReader_6          | 0.01    | root      |                        | index:IndexRangeScan_5                      |
| └─IndexRangeScan_5     | 0.01    | cop[tikv] | table:t1, index:c1(c1) | range:[3,3], keep order:false, stats:pseudo |
+------------------------+---------+-----------+------------------------+---------------------------------------------+
2 rows in set (0.00 sec)

MySQL compatibility

  • FULLTEXT, HASH and SPATIAL indexes are not supported.
  • Descending indexes are not supported (similar to MySQL 5.7).
  • Adding the primary key of the CLUSTERED type to a table is not supported. For more details about the primary key of the CLUSTERED type, refer to clustered index.

See also