DROP INDEX
This statement removes an index from a specified table, marking space as free in TiKV.
Synopsis
- AlterTableDropIndexStmt
- IgnoreOptional
- TableName
- AlterTableDropIndexSpec
- KeyOrIndex
- IfExists
AlterTableDropIndexStmt ::=
'ALTER' IgnoreOptional 'TABLE' AlterTableDropIndexSpec
IgnoreOptional ::=
'IGNORE'?
TableName ::=
Identifier ('.' Identifier)?
AlterTableDropIndexSpec ::=
'DROP' ( KeyOrIndex | 'FOREIGN' 'KEY' ) IfExists Identifier
KeyOrIndex ::=
'KEY'
| 'INDEX'
IfExists ::= ( 'IF' 'EXISTS' )?
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 | 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> CREATE INDEX c1 ON t1 (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> ALTER TABLE t1 DROP INDEX c1;
Query OK, 0 rows affected (0.30 sec)
MySQL compatibility
- Removing the primary key constraint from a column is not supported by default. You can enable the feature by setting the
alter-primary-keyconfiguration item totrue. For details, see alter-primary-key.