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CREATE INDEX

This statement adds a new index to an existing table. It is an alternative syntax to ALTER TABLE .. ADD INDEX, and included for MySQL compatibility.

Synopsis

CreateIndexStmt:

CreateIndexStmt

CreateIndexStmtUnique:

CreateIndexStmtUnique

Identifier:

Identifier

IndexTypeOpt:

IndexTypeOpt

TableName:

TableName

IndexColNameList:

IndexColNameList

IndexOptionList:

IndexOptionList

IndexOption:

IndexOption

Examples

mysql> CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, c1 INT NOT NULL); Query OK, 0 rows affected (0.10 sec) mysql> INSERT INTO t1 (c1) VALUES (1),(2),(3),(4),(5); Query OK, 5 rows affected (0.02 sec) Records: 5 Duplicates: 0 Warnings: 0 mysql> EXPLAIN SELECT * FROM t1 WHERE c1 = 3; +---------------------+----------+------+-------------------------------------------------------------+ | id | count | task | operator info | +---------------------+----------+------+-------------------------------------------------------------+ | TableReader_7 | 10.00 | root | data:Selection_6 | | └─Selection_6 | 10.00 | cop | eq(test.t1.c1, 3) | | └─TableScan_5 | 10000.00 | cop | table:t1, range:[-inf,+inf], keep order:false, stats:pseudo | +---------------------+----------+------+-------------------------------------------------------------+ 3 rows in set (0.00 sec) mysql> CREATE INDEX c1 ON t1 (c1); Query OK, 0 rows affected (0.30 sec) mysql> EXPLAIN SELECT * FROM t1 WHERE c1 = 3; +-------------------+-------+------+-----------------------------------------------------------------+ | id | count | task | operator info | +-------------------+-------+------+-----------------------------------------------------------------+ | IndexReader_6 | 10.00 | root | index:IndexScan_5 | | └─IndexScan_5 | 10.00 | cop | table:t1, index:c1, range:[3,3], keep order:false, stats:pseudo | +-------------------+-------+------+-----------------------------------------------------------------+ 2 rows in set (0.00 sec) mysql> ALTER TABLE t1 DROP INDEX c1; Query OK, 0 rows affected (0.30 sec) mysql> CREATE UNIQUE INDEX c1 ON t1 (c1); Query OK, 0 rows affected (0.31 sec)

Associated session variables

The global variables associated with the CREATE INDEX statement are tidb_ddl_reorg_worker_cnt, tidb_ddl_reorg_batch_size and tidb_ddl_reorg_priority. Refer to TiDB-specific system variables for details.

MySQL compatibility

  • FULLTEXT, HASH and SPATIAL indexes are not supported.
  • Descending indexes are not supported (similar to MySQL 5.7).
  • Adding the primary key constraint to a table is not supported by default. You can enable the feature by setting the alter-primary-key configuration item to true. For details, see alter-primary-key.

See also

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