Question

我在数据库中有行表：

id，kills，deaths，week

我如何选择kills week=1和deaths哪里week=2在一个表中？

Answer 1

您可以使用两个单独的select语句：

SELECT(
    (SELECT kills FROM tablename WHERE week = 1),
    (SELECT deaths FROM tablename WHERE week = 2)
)

这将为周期= 1的杀戮创建一列，为周= 2的死亡创建另一列。

您可以使用UNION关键字将它们组合在一起：

SELECT 'week 1 - kills' as source, kills FROM tablename WHERE week = 1
UNION
SELECT 'week 2 - deaths' as source, deaths FROM tablename WHERE week = 2

这两种方法需要对表进行双重扫描。

如果您需要聚合函数，另一种方法是使用条件子句@Juan Carlos Oropeza的解决方案。但是，正如所指出的那样，将这两个陈述合并为一个可能不是最佳选择。

Answer 2

您可以使用条件聚合

SELECT SUM (CASE WHEN week = 1 THEN kills END) as total_kills_week1, 
       SUM (CASE WHEN week = 2 THEN deaths END) as total_deaths_week2
FROM YourTable

我如何在一个表中使用多个WHERE进行SELECT

2 个答案: