Question

我简化了以下mysql查询，该查询计算table1中的主键作为table2中的外键出现的次数。

SELECT table1.*, COUNT(table2.id) AS 'value'

FROM table1 INNER JOIN table2 ON table1.id = table2.id

WHERE table1.lastname LIKE 'smith'

WHERE table1.firstname LIKE 'john'

GROUP BY table2.id;

我想修改它以便它只选择超过某个阈值的计数，也就是说，如果john smith的id在table2中出现10次，而我的阈值是20，则不会选择他的记录。

Answer 1

GROUP BY table2.id
  HAVING COUNT(table2.id) >= @Threshold

Answer 2

SELECT table1.*,table2.value as value
FROM table1,
(
SELECT table2.id, COUNT(table2.id) AS 'value'

FROM table1 INNER JOIN table2 ON table1.id = table2.id

WHERE table1.lastname LIKE 'smith' AND table1.firstname LIKE 'john'

GROUP BY table2.id
HAVING COUNT(table2.id)>=20
) table2
WHERE table1.id=table2.id;

根据用户定义的限制选择外键计数

2 个答案: