Mysql COUNT和IF用法

Question

我有MySQL表格结构：

| uid     |   itemid
| -------------------
| 1001    |   9999
| 1001    |   8888
| 2002    |   8888
| ...     |   ...

uid 和 itemid 不是唯一列。 Bun uid + itemid是独特的组合。

我需要按itemid计算行数。我使用下一个查询：

SELECT itemid, COUNT(*) 
FROM unlikes 
WHERE itemid IN ('9999', '8888') GROUP BY itemid;

这很有效！

接下来，我需要知道哪一行有具体的uid。我用：

SELECT itemid, COUNT(*), IF (uid = '1001', TRUE, FALSE) toggled 
FROM unlikes 
WHERE itemid IN ('9999', '8888') GROUP BY itemid;'

不行。如果我有多个itemid = 8888，而不是toggled = FALSE。如果组中的一个有uid = 1001;

，我需要切换= TRUE

Answer 1

SELECT itemid, COUNT(*), 
CASE WHEN uid = 1001 THEN TRUE ELSE FALSE end AS toggled 
FROM unlikes 
WHERE itemid IN ('9999', '8888') GROUP BY itemid;