如何编写子句：WHERE num =…对于SELECT COUNT（*）作为num…的语句？

Question

我有陈述

SELECT COUNT(*) as num_requests, ip_address FROM requests
GROUP BY ip_address
ORDER BY num_requests DESC;

当我使用以下子句WHERE num_requests = 3出现语法错误

SELECT COUNT(*) as num_requests, ip_address 
FROM requests
WHERE num_requests = 3
GROUP BY ip_address
ORDER BY num_requests DESC;

“ where子句”中的未知列“ num_requests”

有什么方法可以使用此WHERE子句，而无需对上述返回的整个结果集编写嵌套查询或join语句？

Answer 1

SELECT COUNT(*) as num_requests, ip_address 
FROM requests
GROUP BY ip_address
HAVING num_requests = 3
ORDER BY num_requests DESC

Answer 2

您需要having :)

SELECT COUNT(*) as num_requests, ip_address FROM requests
GROUP BY ip_address
HAVING COUNT(*) = 3
ORDER BY num_requests DESC;

补充说明为什么不能使用WHERE而是HAVING ：带有诸如SUM, MIN,MAX,AVG,COUNT聚合的WHERE无法使用。 因此，您必须使用后者。