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Posted by Ed Murphy on 10/07/88 11:59
Dimitri Furman wrote:
> Consider this script:
>
> USE pubs
> GO
>
> IF 1 = ALL (SELECT contract FROM dbo.authors WHERE state = 'CA')
> PRINT 'TRUE'
> ELSE
> PRINT 'FALSE'
>
> This, as expected, prints FALSE, since not all authors in CA are under
> contract. Now, if the script is changed as follows:
>
> USE pubs
> GO
>
> IF 1 = ALL (SELECT contract FROM dbo.authors WHERE state = '')
> PRINT 'TRUE'
> ELSE
> PRINT 'FALSE'
>
> then the result is TRUE. In other words, the expression evaluates to TRUE
> when the select statement produces an empty set, which doesn't make sense
> to me. Even more interesting, the expression
>
> NULL = ALL (SELECT contract FROM dbo.authors WHERE state = '')
>
> still evaluates to TRUE (ANSI_NULLS is ON).
>
> Can anyone explain these results? Is this the expected behavior in the SQL
> standard, or something that is specific to SQL Server? Thanks.
It's vacuously true because there are no elements in the set to
produce a non-equality.
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