MySQL8 distinct去除重复行

distinct 过滤重复行

mysql> SELECT DISTINCT srcuser FROM mail;
+---------+
| srcuser |
+---------+
| barb    |
| tricia  |
| phil    |
| gene    |
+---------+
4 rows in set (0.00 sec)

统计唯一结果的数量，使用count(distinct)

mysql> SELECT COUNT(DISTINCT srcuser) FROM mail;
+-------------------------+
| COUNT(DISTINCT srcuser) |
+-------------------------+
|                       4 |
+-------------------------+
1 row in set (0.00 sec)

DISTINCT关键字也可以使用多列输出

mysql> SELECT DISTINCT YEAR(t),MONTH(t),DAYOFMONTH(t) FROM mail;
+---------+----------+---------------+
| YEAR(t) | MONTH(t) | DAYOFMONTH(t) |
+---------+----------+---------------+
|    2014 |        5 |            11 |
|    2014 |        5 |            12 |
|    2014 |        5 |            14 |
|    2014 |        5 |            15 |
|    2014 |        5 |            16 |
|    2014 |        5 |            19 |
+---------+----------+---------------+
6 rows in set (0.00 sec)