# **DROP INDEX**

## **语法说明**

该语句用于从当前所选的表中删除索引，如果索引不存在则会报错，除非使用 `IF EXISTS` 修饰符。

## **语法结构**

```sql
DROP INDEX index_name ON tbl_name
```

## **示例**

```text
create table t5(a int, b int, unique key(a));
mysql> show create table t5;
+-------+----------------------------------------------------------------------------------------+
| Table | Create Table                                                                           |
+-------+----------------------------------------------------------------------------------------+
| t5    | CREATE TABLE `t5` (
`a` INT DEFAULT NULL,
`b` INT DEFAULT NULL,
UNIQUE KEY `a` (`a`)
) |
+-------+----------------------------------------------------------------------------------------+
1 row in set (0.01 sec)

create index b on t5(b);
mysql> show create table t5;
+-------+-------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                          |
+-------+-------------------------------------------------------------------------------------------------------+
| t5    | CREATE TABLE `t5` (
`a` INT DEFAULT NULL,
`b` INT DEFAULT NULL,
UNIQUE KEY `a` (`a`),
KEY `b` (`b`)
) |
+-------+-------------------------------------------------------------------------------------------------------+
1 row in set (0.02 sec)

drop index b on t5;
mysql> show create table t5;
+-------+----------------------------------------------------------------------------------------+
| Table | Create Table                                                                           |
+-------+----------------------------------------------------------------------------------------+
| t5    | CREATE TABLE `t5` (
`a` INT DEFAULT NULL,
`b` INT DEFAULT NULL,
UNIQUE KEY `a` (`a`)
) |
+-------+----------------------------------------------------------------------------------------+
1 row in set (0.02 sec)
```