SQL 检查所有行的列中的值是否正好是值
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Check if value in column for all rows is exactly value
提问by gilhanan
For example, I want follow the number 2 as target
例如，我想按照数字 2 作为目标
This should return positive indication:
这应该返回积极的迹象：
ID Status
123 2
432 2
531 2
123 2
This should return negative indication:
这应该返回否定指示：
ID Status
123 1
432 3
531 2
123 2
This should return negative indication:
这应该返回否定指示：
ID Status
123 1
432 1
531 1
123 1
Thanks
谢谢
回答by Martin Smith
EXISTSshould be used in preference to COUNTso it can return as soon as the first non matching row is found.
EXISTS应该优先使用 toCOUNT以便它可以在找到第一个不匹配的行后立即返回。
SELECT CASE
WHEN NOT EXISTS(SELECT *
FROM your_table
WHERE status <> 2) THEN 'Y'
ELSE 'N'
END AS your_result
You don't state RDBMS. You might need to append FROM DUALonto the end of the above dependant on flavour.
您没有说明 RDBMS。FROM DUAL根据口味，您可能需要附加到上述内容的末尾。
回答by Tim
select (select count(distinct status) from T) = 1
will return 1 or 0 (i.e. true or false) depending on whether all of the rows have the same value in Status or not. If you have to deal with NULL values in status:
将返回 1 或 0（即 true 或 false），具体取决于所有行在 Status 中是否具有相同的值。如果您必须处理状态中的 NULL 值：
select exists
( select status from T where status <> 2 or status is null)
as StatusContainsOtherThanTwoOrNullValue
回答by RedGrittyBrick
select count(*) where Status != 2
select count(*) where Status != 2
