MySQL聚合函数如何与MySQL IF()函数结合？
将MySQL聚合函数与MySQLIF()函数结合起来对获得我们想要的特定输出非常有帮助。请看以下查询，这些查询将功能与功能结合SUM()和COUNT()聚合IF()。
示例
mysql> Select SUM(IF(Language = 'English', 1, 0)) As English, SUM(IF(Language <> 'English',1,0)) AS "Non-English" from Students; +---------+-------------+ | English | Non-English | +---------+-------------+ | 5 | 4 | +---------+-------------+ 1 row in set (0.00 sec)
上面的查询将SUM()聚合函数与IF()函数结合起来，以从“学生”表中获取英语学生和非英语学生的输出。
mysql> Select COUNT(IF(country = 'USA', 1, NULL))AS USA,
-> COUNT(IF(country = 'UK', 1, NULL))AS UK,
-> COUNT(IF(country = 'France', 1, NULL))AS France,
-> COUNT(IF(country = 'Russia', 1, NULL))AS Russia,
-> COUNT(IF(country = 'Australia', 1, NULL))AS Australia,
-> COUNT(IF(country = 'INDIA', 1, NULL))AS INDIA,
-> COUNT(IF(country = 'NZ', 1, NULL))AS NZ FROM Students;
+-----+----+--------+--------+-----------+-------+----+
| USA | UK | France | Russia | Australia | INDIA | NZ |
+-----+----+--------+--------+-----------+-------+----+
| 2 | 1 | 1 | 1 | 1 | 2 | 1 |
+-----+----+--------+--------+-----------+-------+----+
1 row in set (0.07 sec)上面的查询将COUNT()聚合函数与IF()函数结合在一起，以从“学生”表中获取多个国家/地区的输出。