drop-index.md

title	summary	category
DROP INDEX	TiDB 数据库中 DROP INDEX 的使用概况。	reference

DROP INDEX

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

AlterTableStmt:

AlterTableSpec:

KeyOrIndex:

Identifier:

示例

{{< copyable "sql" >}}

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

Query OK, 0 rows affected (0.10 sec)

{{< copyable "sql" >}}

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

Query OK, 5 rows affected (0.02 sec)
Records: 5  Duplicates: 0  Warnings: 0

{{< copyable "sql" >}}

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)

{{< copyable "sql" >}}

CREATE INDEX c1 ON t1 (c1);

Query OK, 0 rows affected (0.30 sec)

{{< copyable "sql" >}}

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)

{{< copyable "sql" >}}

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