mysql - 子查询不提供输出

Question

我正在尝试运行一个查询，该查询返回一个 ID 列表，这些 ID 在名为 Hospital 的表中出现超过 3 次。到目前为止，我想出了这个:

SELECT doctorID
FROM Hospital 
WHERE doctorID IN

(SELECT temp.doctorID, count(temp.doctorID) as frequency
FROM Hospital as temp
GROUP BY temp.doctorID
HAVING frequency >3);

但由于某些原因，我在运行时遇到错误

Code: 1241. Operand should contain 1 column(s)

当我环顾四周时，这似乎是一个常见的错误，但我找不到适用于我的现有解决方案。当我单独运行括号中的查询时，它工作正常。那么它为什么不能用作子查询呢？

Answer 1

从子查询中删除第二列，将 count() 移到 HAVING 子句中:

SELECT doctorID
FROM Hospital 
WHERE doctorID IN

(SELECT temp.doctorID
FROM Hospital AS temp
GROUP BY temp.doctorID
HAVING count(temp.doctorID) > 3);

您可以更简单地获得相同的结果，而无需子查询:

SELECT doctorID
FROM   Hospital
GROUP  BY doctorID
HAVING count(doctorID) > 3;