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
- AlterTableSpec
- ColumnKeywordOpt
- ColumnDef
- ColumnPosition
AlterTableStmt ::=
'ALTER' IgnoreOptional 'TABLE' TableName ( AlterTableSpecListOpt AlterTablePartitionOpt | 'ANALYZE' 'PARTITION' PartitionNameList ( 'INDEX' IndexNameList )? AnalyzeOptionListOpt )
AlterTableSpec ::=
TableOptionList
| 'SET' 'TIFLASH' 'REPLICA' LengthNum LocationLabelList
| 'CONVERT' 'TO' CharsetKw ( CharsetName | 'DEFAULT' ) OptCollate
| 'ADD' ( ColumnKeywordOpt IfNotExists ( ColumnDef ColumnPosition | '(' TableElementList ')' ) | Constraint | 'PARTITION' IfNotExists NoWriteToBinLogAliasOpt ( PartitionDefinitionListOpt | 'PARTITIONS' NUM ) )
| ( ( 'CHECK' | 'TRUNCATE' ) 'PARTITION' | ( 'OPTIMIZE' | 'REPAIR' | 'REBUILD' ) 'PARTITION' NoWriteToBinLogAliasOpt ) AllOrPartitionNameList
| 'COALESCE' 'PARTITION' NoWriteToBinLogAliasOpt NUM
| 'DROP' ( ColumnKeywordOpt IfExists ColumnName RestrictOrCascadeOpt | 'PRIMARY' 'KEY' | 'PARTITION' IfExists PartitionNameList | ( KeyOrIndex IfExists | 'CHECK' ) Identifier | 'FOREIGN' 'KEY' IfExists Symbol )
| 'EXCHANGE' 'PARTITION' Identifier 'WITH' 'TABLE' TableName WithValidationOpt
| ( 'IMPORT' | 'DISCARD' ) ( 'PARTITION' AllOrPartitionNameList )? 'TABLESPACE'
| 'REORGANIZE' 'PARTITION' NoWriteToBinLogAliasOpt ReorganizePartitionRuleOpt
| 'ORDER' 'BY' AlterOrderItem ( ',' AlterOrderItem )*
| ( 'DISABLE' | 'ENABLE' ) 'KEYS'
| ( 'MODIFY' ColumnKeywordOpt IfExists | 'CHANGE' ColumnKeywordOpt IfExists ColumnName ) ColumnDef ColumnPosition
| 'ALTER' ( ColumnKeywordOpt ColumnName ( 'SET' 'DEFAULT' ( SignedLiteral | '(' Expression ')' ) | 'DROP' 'DEFAULT' ) | 'CHECK' Identifier EnforcedOrNot | 'INDEX' Identifier IndexInvisible )
| 'RENAME' ( ( 'COLUMN' | KeyOrIndex ) Identifier 'TO' Identifier | ( 'TO' | '='? | 'AS' ) TableName )
| LockClause
| AlgorithmClause
| 'FORCE'
| ( 'WITH' | 'WITHOUT' ) 'VALIDATION'
| 'SECONDARY_LOAD'
| 'SECONDARY_UNLOAD'
ColumnKeywordOpt ::=
'COLUMN'?
ColumnDef ::=
ColumnName ( Type | 'SERIAL' ) ColumnOptionListOpt
ColumnPosition ::=
( 'FIRST' | 'AFTER' ColumnName )?
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 | 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)
ALTER TABLE t1 ADD INDEX (c1);
Query OK, 0 rows affected (0.30 sec)
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 兼容性
- 不支持
FULLTEXT，HASH和SPATIAL索引。 - 不支持降序索引（类似于 MySQL 5.7）。
- 目前尚不支持同时添加多个索引。
- 默认无法向表中添加
PRIMARY KEY，在开启alter-primary-key配置项后可支持此功能，详情参考：alter-primary-key。