Question

美好的一天。

表中有数据：

id UserIdn CommentIdn LikeIdn NewsIdn Type IsFavorite DateCreate

1  527464             613895  748153  up   yes   0000-00-00 00:00:00

对于获取计数值，我使用代码：

SELECT 
count(Type='up') as CountUp, 
count(Type='down') as CountDown 
FROM Likes WHERE NewsIdn = '748153'

但结果是

CountUp  CountDown
   1       0

我得到了

CountUp  CountDown
    1       1

请告诉我为什么我的结果不正确？如何查询是对的？

Answer 1

在sum（）中尝试使用案例。

SELECT SUM(CASE WHEN Type = 'up' THEN 1 ELSE 0 END) as 'count_up'
...

Answer 2

例如Type='up'函数中的COUNT()为false（0）或true（1）。但COUNT()并不关心这一点，只是看到有一排。请改用SUM()：

SELECT 
COALESCE(SUM(Type='up'), 0) as CountUp, 
COALESCE(SUM(Type='down'), 0) as CountDown 
FROM Likes WHERE NewsIdn = '748153'

Answer 3

试试这个......

SELECT
SUM(CASE WHEN Type='up' AND Type IS NOT NULL THEN 1 ELSE 0 END) as CountUp,
SUM(CASE WHEN Type='down' AND Type IS NOT NULL THEN 1 ELSE 0 END) as CountDown
FROM Likes
WHERE NewsIdn = '748153'

为什么查询给出不正确的结果？

3 个答案: