未定义列的Where子句

Question

我正在撰写查询，但遇到了问题。

select name, address, count(BL.card_no) 
from Book_Loans BL 
inner join Borrower B on BL.card_no = B.card_no 
where count(BL.card_no) > 1 group by name;

这不起作用，因为我不能使用“where count（BL.card_no）＆gt; 1”，因为它说“组功能的使用无效”。但我需要确保只显示大于1的卡号，我还能怎么做呢？

Answer 1

您必须将谓词放在HAVING子句中：

select name, address, count(BL.card_no) 
from Book_Loans BL 
inner join Borrower B on BL.card_no = B.card_no 
group by name
having count(BL.card_no) > 1;

Answer 2

用于聚合函数使用而不是在哪里

select name, address, count(BL.card_no) 
from Book_Loans BL 
inner join Borrower B on BL.card_no = B.card_no 
group by name
having  count(BL.card_no) > 1;