Question

我在尝试使用聚合函数结果作为条件时遇到问题。基本上，我需要选择具有＆＃34;查看计数＆＃34;的行。超过3.这是有效的代码：

SELECT b.BranchNo AS "Branch Number",
p.PropertyNo || ', ' || p.PostCode || ', ' || p.City || ', ' || p.Street AS "Object address" , count(v.ViewDate) as "View count"
FROM Branch b INNER JOIN PropertyForRent p ON b.BranchNo=p.PropertyBranchNo 
INNER JOIN Viewing v ON p.PropertyNo=v.ViewPropertyNo WHERE v.ViewDate>='2014-01-01' 
GROUP BY b.BranchNo,  p.PropertyNo;

我试图使用类似的东西：

HAVING count(v.ViewDate)>=3

但这显然不起作用。有没有办法在不使用子查询的情况下制作这种条件？

Answer 1

您select中的字段似乎与group by不匹配，但除此之外，“基于汇总的条件”正是having子句的内容是为了。例如，此查询应该有效：

SELECT 
b.BranchNo AS "Branch Number",
p.PropertyNo || ', ' || p.PostCode || ', ' || p.City || ', ' || p.Street AS "Object address" , 
count(v.ViewDate) as "View count"
FROM Branch b INNER JOIN PropertyForRent p ON b.BranchNo=p.PropertyBranchNo 
INNER JOIN Viewing v ON p.PropertyNo=v.ViewPropertyNo WHERE v.ViewDate>='2014-01-01' 
GROUP BY b.BranchNo, p.PropertyNo, p.PostCode, p.City, p.Street
HAVING count(v.ViewDate) >= 3;

Answer 2

您需要在查看表子查询中进行分组以获取计数。然后加入。

SELECT b.BranchNo AS [Branch Number],
    p.PropertyNo + ', ' + p.PostCode + ', ' + p.City + ', ' + p.Street AS [Object address],
    v.ViewCount

FROM Branch b 
    INNER JOIN PropertyForRent p ON b.BranchNo=p.PropertyBranchNo 
    INNER JOIN (SELECT ViewPropertyNo, COUNT(*) as ViewCount 
                FROM Viewing 
                WHERE v.ViewDate>='2014-01-01' 
                GROUP BY ViewPropertyNo
                ) AS v ON p.PropertyNo = v.ViewPropertyNo 
WHERE v.ViewCount >= 3;

聚合函数作为条件

2 个答案: