MySQL聚合函数如何与MySQL IF()函数结合？

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)

上述查询将SUM()聚合函数与IF()函数结合使用，从“学生”表中获取英语母语学生和非英语母语学生的输出。

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()函数结合起来，以从“Students”表中获取国家数量的输出。

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