sql - 一行sql中的多个where子句

Question

我想采用以下语句并将其融合为一个查询。

SELECT COUNT(*) AS count1 WHERE Month='11' AND Flag = 1
SELECT COUNT(*) AS count2 WHERE Month='11' AND Flag = 2
SELECT COUNT(*) AS count1 WHERE Month='12' AND Flag = 1
    SELECT COUNT(*) AS count2 WHERE Month='12' AND Flag = 2

我希望它显示为一个查询，其中包含 count1 和 count2 列以及第 11 个月和第 12 个月的行。

这有语法吗？

Answer 1

您可以组合 SUM和 CASE一次性获得各种计数:

SELECT
    Month,
    SUM(CASE WHEN Flag=1 THEN 1 ELSE 0 END) as count1,
    SUM(CASE WHEN Flag=2 THEN 1 ELSE 0 END) as count2
from
    ...
WHERE Month in ('11','12')
GROUP BY
    Month /* Other columns? */