Question

我有这个问题：

SELECT
count( case when EXISTS (
        SELECT *
        FROM   business_log bl, subject su
        WHERE  su.ID_SUBJECT = s.ID_SUBJECT
        AND    bl.id_subject = su.id_subject
        AND    bl.value = 'Solved'
        )
then 1 else null end) num_solved
FROM subject s

一个主题不止一次是可能的......解决了这个问题。在表BUSINESS_LOG中我想只计算一个主题解决的一行。由于其他计数，我必须在主查询中仅使用SUBJECT表。

Answer 1

business_log：

id_business_log id_subject value 
1 1 Solved 
2 2 Evidented 
3 3 Evidented 
4 1 Solved

主题

ID_SUBJECT
1
2
3

使用不带CASE的COUNT查询

SELECT
ID_SUBJECT,
(
    SELECT count(*)
    FROM   business_log bl
    WHERE  bl.id_subject = s.id_subject
    AND    bl.value = 'Solved'
) as num_solved
FROM subject s

返回

ID_SUBJECT  num_solved
1   2
2   0
3   0

包含CASE的原始查询，但没有COUNT

SELECT
ID_SUBJECT,
case when EXISTS (
            SELECT *
            FROM   business_log bl
            WHERE  bl.id_subject = s.id_subject
            AND    bl.value = 'Solved'
        )
then 1 else null end num_solved
FROM subject s

返回

ID_SUBJECT  num_solved
1   1
2   NULL
3   NULL

计算具有相同ID的相同值的多行中的一行

1 个答案: