去重

在MySQL中需要查询表中不重复的记录时，可以使用distinct关键字过滤重复记录。

语法：

select distinct [,...,] from ;

数据表如下：

mysql> select * from emp;

+-------+--------+------------+------+------------+------+------+--------+

| empno | ename | job | mgr | hiredate | sal | comm | deptno |

+-------+--------+------------+------+------------+------+------+--------+

| 7369 | smith | clerk | 7902 | 1980-12-17 | 800 | NULL | 20 |

| 7499 | allen | salesman | 7698 | 1981-02-20 | 1600 | 300 | 30 |

| 7521 | ward | salesman | 7698 | 1981-02-22 | 1250 | 500 | 30 |

| 7566 | jones | manager | 7839 | 1981-04-02 | 2975 | NULL | 20 |

| 7654 | martin | salesman | 7698 | 1981-09-28 | 1250 | 1400 | 30 |<