我有一个表,该表的列名为ReportTypeId。我想选择ReportTypeId = 1的行,但是如果对此不存在任何行,那么我希望ReportTypeId =2。我正在尝试使用WHEN EXISTS,但是我不知道如何选择多于一列的内容。我想写一个看起来像这样的查询:
SELECT CASE
WHEN EXISTS (SELECT PerformanceReport FROM ReportData
WHERE (ReportId = 79 and ReportTypeId = 1))
THEN (select * from ReferenceData
where ReportTypeId = 1)
ELSE (select * from ReferenceData
where ReportTypeId = 2)
END
但是因为我试图返回多个列,所以它不起作用。有没有一种方法可以基于数据是否存在创建基于WHERE语句的查询?
答案 0 :(得分:1)
您可以使用以下解决方案:
SELECT *
FROM ReferenceData
WHERE (
ReportTypeId = 1
AND EXISTS (SELECT * FROM ReportData WHERE ReportTypeId = 1 AND ReportId = 79)
) OR (
ReportTypeId = 2
AND NOT EXISTS (SELECT * FROM ReportData WHERE ReportTypeId = 1 AND ReportId = 79)
)
您可以使用JOIN
对此进行优化:
SELECT ReferenceData.*
FROM ReferenceData JOIN (
SELECT EXISTS (SELECT * FROM ReportData WHERE ReportTypeId = 1 AND ReportId = 79) AS state
) isAvailable
WHERE (
ReportTypeId = 1 AND isAvailable.state = 1
) OR (
ReportTypeId = 2 AND isAvailable.state = 0
)
您可以使用JOIN
添加多个支票:
SELECT ReferenceData.*
FROM ReferenceData JOIN (
SELECT EXISTS (SELECT * FROM ReportData WHERE ReportTypeId = 1 AND ReportId = 79) AS state
) avail1 JOIN (
SELECT EXISTS (SELECT * FROM ReportData WHERE ReportTypeId = 2 AND ReportId = 79) AS state
) avail2 JOIN (
SELECT EXISTS (SELECT * FROM ReportData WHERE ReportTypeId = 3 AND ReportId = 79) AS state
) avail3
WHERE (
ReportTypeId = 1 AND avail1.state = 1
) OR (
ReportTypeId = 2 AND avail1.state = 0 AND avail2.state = 1
) OR (
ReportTypeId = 3 AND avail1.state = 0 AND avail2.state = 0 AND avail3.state = 1
) OR (
ReportTypeId = 4 AND avail1.state = 0 AND avail2.state = 0 AND avail3.state = 0
)
答案 1 :(得分:1)
如果可以订购RecordTypeId
**,则可以使用以下
SELECT PerformanceReport
FROM ReferenceData
WHERE ReportTypeId = (
SELECT MIN(ReportTypeId)
FROM ReportData
WHERE ReportTypeId IN (1, 2)
AND ReportId = 79
)
**按顺序排列,我的意思是MIN
聚合函数将返回预期的结果。对于整数,这是有道理的,但是,如果您的报表类型ID是文本uuid,则MIN
仍然可以工作,但不会给您预期的结果,因为它将以词法顺序返回最小ID。
答案 2 :(得分:1)
您似乎想要:
SELECT refd.*
FROM ReferenceData refd
WHERE (refd.ReportType = 1 AND
EXISTS (SELECT 1
FROM ReportData repd
WHERE repd.ReportId IN (1, 79)
)
) OR
(refd.ReportType = 2 AND
EXISTS (SELECT 1
FROM ReportData repd
WHERE repd.ReportId NOT IN (1, 79)
)
)