ADD INDEX
ALTER TABLE.. ADD INDEX 语句用于在已有表中添加一个索引。在 TiDB 中，ADD INDEX 为在线操作，不会阻塞表中的数据读写。
语法图
- 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'
示例
CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, c1 INT NOT NULL);
Query OK, 0 rows affected (0.11 sec)
INSERT INTO t1 (c1) VALUES (1),(2),(3),(4),(5);
Query OK, 5 rows affected (0.03 sec)
Records: 5 Duplicates: 0 Warnings: 0
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)
ALTER TABLE t1 ADD INDEX (c1);
Query OK, 0 rows affected (0.30 sec)
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 兼容性
- 为了兼容 MySQL，TiDB 在语法上支持
HASH、BTREE和RTREE等索引类型，但会忽略它们。 - 不支持
SPATIAL索引。 - TiDB 支持解析
FULLTEXT语法，但不支持使用FULLTEXT索引。 - 不支持降序索引（类似于 MySQL 5.7）。
- 无法向表中添加
CLUSTERED类型的PRIMARY KEY。要了解关于CLUSTERED主键的详细信息，请参考聚簇索引。