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Jeroen W. Pluimers on .NET, C#, Delphi, databases, and personal interests

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Firebird; testing for NULL and equality in practice: IS [NOT] DISTINCT FROM

Posted by jpluimers on 2017/06/14

Boy, I totally missed that this was introduced back then in Firebird 2.0:

 In Firebird 2 and higher, you test for null-encompassing equality with DISTINCT. This has already been discussed, but here’s a quick recap. Two expressions are considered:
  • DISTINCT if they have different values or if one of them is NULL and the other isn’t;
  • NOT DISTINCT if they have the same value or if both of them are NULL.

[NOT] DISTINCT always returns true or false, never NULL or something else. Examples:

if (A is distinct from B) then...
if (Buyer1 is not distinct from Buyer2) then...


Source: Testing for NULL and equality in practice


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