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
- AddIndexSpec
- IndexPartSpecification
- IndexOption
- IndexType
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
andSPATIAL
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 theCLUSTERED
type, refer to clustered index.