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
  3. IgnoreOptional ::=
  4. 'IGNORE'?
  5. TableName ::=
  6. Identifier ('.' Identifier)?
  7. AlterTableDropIndexSpec ::=
  8. 'DROP' ( KeyOrIndex | 'FOREIGN' 'KEY' ) IfExists Identifier
  9. KeyOrIndex ::=
  10. 'KEY'
  11. | 'INDEX'
  12. 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