Question

DROP INDEX 语句用于从指定的表中删除索引，并在 TiKV 中将空间标记为释放。

语法图

AlterTableDropIndexStmt:

IgnoreOptional:

TableName:

AlterTableDropIndexSpec:

KeyOrIndex:

IfExists:

示例

CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, c1 INT NOT NULL);

Query OK, 0 rows affected (0.10 sec)

INSERT INTO t1 (c1) VALUES (1),(2),(3),(4),(5);

Query OK, 5 rows affected (0.02 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)

CREATE INDEX c1 ON t1 (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)

ALTER TABLE t1 DROP INDEX c1;

Query OK, 0 rows affected (0.30 sec)

MySQL 兼容性

• 默认不支持删除 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。

另请参阅

• SHOW INDEX
• CREATE INDEX
• ADD INDEX
• RENAME INDEX