distinct去重

去重查询

select distinct 字段 from 数据库

（1）查询 tb_students_info 表中所有 age 的执行结果如下所示。

mysql> SELECT age FROM tb_students_info;
+------+
| age  |
+------+
|   25 |
|   23 |
|   23 |
|   22 |
|   24 |
|   21 |
|   22 |
|   23 |
|   22 |
|   23 |
+------+
10 rows in set (0.00 sec)


（2）查询 tb_students_info 表中 age 字段的值，返回 age 字段的值且不得重复，

mysql> SELECT  DISTINCT age
    -> FROM tb_students_info;
+------+
| age  |
+------+
|   25 |
|   23 |
|   22 |
|   24 |
|   21 |
+------+
5 rows in set (0.11 sec)