Mysql COUNT 和 IF 用法

Question

我有 MySQL 表，其结构为:

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

uid 和 itemid 不是唯一的列。 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;

这有效!

接下来，我需要知道哪一行有具体的 uid。我使用:

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

不工作。如果我有不止一行 itemid = 8888，则切换 = FALSE。如果组中有一个 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;