sql - WHERE 子句或 HAVING 中的 COUNT？

Question

这基本上就是我想要实现的目标；

SELECT 
COUNT(DISTINCT No) 
FROM 
Table 
WHERE 
(Type = 1 AND COUNT(DISTINCT No) > Num) 
OR (Type = 2 AND COUNT(DISTINCT No) > Num) 
GROUP BY
Week

实现这一目标的最佳方法是什么？

谢谢

Answer 1

任何聚合比较都需要进入 Group By 之后的 HAVING 子句。请记住，根据非聚合条件的放置位置，您可能会得到不同的结果，因为您将通过 WHERE 聚合包含/排除的内容。

即

SELECT COUNT(DISTINCT No) 
FROM Table 
WHERE Type = 1
GROUP BY Week
HAVING COUNT(DISTINCT No) > Num

可能与

不同

SELECT COUNT(DISTINCT No) 
FROM Table 
GROUP BY Week
HAVING COUNT(DISTINCT No) > Num
AND Type = 1