How Can I Simulate IS DISTINCT FROM and IS NOT DISTINCT FROM in SQL Server 2008R2?

Rewriting IS DISTINCT FROM and IS NOT DISTINCT FROM Predicates in SQL Server 2008R2

In SQL Server 2008R2, the standard IS DISTINCT FROM and IS NOT DISTINCT FROM operators are not supported. This poses a problem for users who need to compare values and obtain definitive results of either True or False instead of the default Unknown.

Rewriting Alternatives

To emulate the IS DISTINCT FROM and IS NOT DISTINCT FROM predicates, the following expressions can be used:

• Rewriting IS DISTINCT FROM:

((a <> b OR a IS NULL OR b IS NULL) AND NOT (a IS NULL AND b IS NULL))

• Rewriting IS NOT DISTINCT FROM:

(NOT (a <> b OR a IS NULL OR b IS NULL) OR (a IS NULL AND b IS NULL))

These expressions effectively determine if the values are not equal or if either value is null. If so, then the returned result is True; otherwise, it is False.

Avoiding Common Pitfalls

It's important to note that the following expression does not correctly rewrite IS DISTINCT FROM:

FALSE OR NULL

In SQL Server, FALSE OR NULL evaluates to Unknown, which is not the desired result. Therefore, it is crucial to use the expressions provided above for accurate rewriting.

Conclusion

By utilizing these rewritten expressions, SQL Server 2008R2 users can achieve the same functionality as IS DISTINCT FROM and IS NOT DISTINCT FROM, ensuring that comparisons always return definitive results.

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