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

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

  1. AlterTableDropIndexStmt ::=
  2.     'ALTER' IgnoreOptional 'TABLE' AlterTableDropIndexSpec
  4. IgnoreOptional ::=
  5.     'IGNORE'?
  7. TableName ::=
  8.     Identifier ('.' Identifier)?
  10. AlterTableDropIndexSpec ::=
  11.     'DROP' ( KeyOrIndex | 'FOREIGN' 'KEY' ) IfExists Identifier
  13. KeyOrIndex ::=
  14.     'KEY'
  15. |   'INDEX'
  17. IfExists ::= ( 'IF' 'EXISTS' )?

示例

  1. CREATE TABLE t1 (id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, c1 INT NOT NULL);
  1. Query OK, 0 rows affected (0.10 sec)
  1. INSERT INTO t1 (c1) VALUES (1),(2),(3),(4),(5);
  1. Query OK, 5 rows affected (0.02 sec)
  2. Records: 5  Duplicates: 0  Warnings: 0
  1. EXPLAIN SELECT * FROM t1 WHERE c1 = 3;
  1. +-------------------------+----------+-----------+---------------+--------------------------------+
  2. | id                      | estRows  | task      | access object | operator info                  |
  3. +-------------------------+----------+-----------+---------------+--------------------------------+
  4. | TableReader_7           | 10.00    | root      |               | data:Selection_6               |
  5. | └─Selection_6           | 10.00    | cop[tikv] |               | eq(test.t1.c1, 3)              |
  6. |   └─TableFullScan_5     | 10000.00 | cop[tikv] | table:t1      | keep order:false, stats:pseudo |
  7. +-------------------------+----------+-----------+---------------+--------------------------------+
  8. 3 rows in set (0.00 sec)
  1. CREATE INDEX c1 ON t1 (c1);
  1. Query OK, 0 rows affected (0.30 sec)
  1. EXPLAIN SELECT * FROM t1 WHERE c1 = 3;
  1. +------------------------+---------+-----------+------------------------+---------------------------------------------+
  2. | id                     | estRows | task      | access object          | operator info                               |
  3. +------------------------+---------+-----------+------------------------+---------------------------------------------+
  4. | IndexReader_6          | 0.01    | root      |                        | index:IndexRangeScan_5                      |
  5. | └─IndexRangeScan_5     | 0.01    | cop[tikv] | table:t1, index:c1(c1) | range:[3,3], keep order:false, stats:pseudo |
  6. +------------------------+---------+-----------+------------------------+---------------------------------------------+
  7. 2 rows in set (0.00 sec)
  1. ALTER TABLE t1 DROP INDEX c1;
  1. Query OK, 0 rows affected (0.30 sec)

MySQL 兼容性

  • 不支持删除 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。

另请参阅