Question

我在同一个表中运行了两个查询：

SELECT id, COUNT(up) 
FROM comentarios 
WHERE up = 1
GROUP BY id

和

SELECT id, COUNT(down) 
FROM comentarios 
WHERE down = 2
GROUP BY id

我尝试了类似的东西但是没有用

SELECT t1.id, COUNT(t1.up), t2.id, COUNT(t2.down)
FROM (SELECT id, up FROM comentarios WHERE up = 1 GROUP BY id) t1
JOIN (SELECT id, down FROM comentarios WHERE down = 2 GROUP BY id) t2

ON t1.id = t2.id

也许需要一个完整的外部加入？

在MySQL中执行此操作的最佳方法是什么？

Answer 1

select id, 
    sum(case when up = 1 then 1 end) as UpCount,
    sum(case when down = 2 then 1 end) as DownCount
from comentarios  
group by id

Answer 2

SELECT id,
       SUM(CASE WHEN up = 1 THEN 1 ELSE 0 END) AS UpCount,
       SUM(CASE WHEN down = 2 THEN 1 ELSE 0 END) AS DownCount
    FROM comentarios
    GROUP BY id

使用来自MySQL中同一个表的COUNT加入两个查询

2 个答案: