MySql:是否可以 'SUM IF' 或 'COUNT IF' ？

Question

我有一列“小时”我有一列“种类”(可以是 1,2 或 3)

我想做这样的事情:

SELECT count(id), SUM(hour) as totHour, SUM( IF ( kind = 1, 1, 0 ) ) as countKindOne

或

SELECT count(id), SUM(hour) as totHour, COUNT( IF ( kind = 1 ) ) as countKindOne

但是 mysql 告诉我我有一个错误...错误是什么!？

请参阅此 stackoverflow 主题:MySQL SUM IF field b = field a

..我无法回复这个...

Answer 1

您可以使用 CASE 语句:

SELECT count(id), 
    SUM(hour) as totHour, 
    SUM(case when kind = 1 then 1 else 0 end) as countKindOne