mysql - 将多个查询与计数和组结合起来

Question

如何将下面的两个 mysql 查询组合成一个查询？

SELECT R12NC,  COUNT(*) AS `count1` FROM alink where Option_a = 1 GROUP BY  R12NC
SELECT R12NC,  COUNT(*) AS `count2` FROM alink where Option_x = 1 GROUP BY  R12NC

Answer 1

通过使用case嵌套在聚合函数中的语句：

SELECT R12NC,
       sum(case when Option_a = 1 then 1 else 0 end) as `count1`,
       sum(case when Option_x = 1 then 1 else 0 end) as `count2`
FROM alink
GROUP BY  R12NC

Answer 2

两种方式。如果您只想要两列，请使用 UNION

SELECT R12NC,  COUNT(*) AS `count1` FROM alink where Option_a = 1 GROUP BY  R12NC
UNION
SELECT R12NC,  COUNT(*) AS `count2` FROM alink where Option_x = 1 GROUP BY  R12NC

如果您想要 3 列，则类似于：

SELECT R12NC, SUM(CASE WHEN Option_a = 1 THEN 1 ELSE 0 END) as `count1`, 
    SUM(CASE WHEN Option_x = 1 THEN 1 ELSE 0 END) as `count2`
FROM alink
GROUP BY  R12NC