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.

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

• TiDB accepts index types such as HASH, BTREE and RTREE in syntax for compatibility with MySQL, but ignores them.
• SPATIAL indexes are not supported.
• TiDB supports parsing the FULLTEXT syntax but does not support using the FULLTEXT indexes.
• 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

• Index Selection
• Wrong Index Solution
• CREATE INDEX
• DROP INDEX
• RENAME INDEX
• ALTER INDEX
• ADD COLUMN
• CREATE TABLE
• EXPLAIN
• TiDB Distributed eXecution Framework (DXF)