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

Emulating IS DISTINCT FROM and IS NOT DISTINCT FROM in SQL Server 2008 R2

SQL Server 2008 R2 lacks direct support for IS DISTINCT FROM and IS NOT DISTINCT FROM. However, we can achieve the same functionality using alternative SQL expressions.

IS DISTINCT FROM returns TRUE if the operands are unequal, or if either operand is NULL. IS NOT DISTINCT FROM returns TRUE if the operands are equal, or if both operands are NULL.

Here's how to replicate these operators:

• Replicating IS DISTINCT FROM:

<code class="language-sql">(a <> b OR a IS NULL OR b IS NULL) AND NOT (a IS NULL AND b IS NULL)</code>

• Replicating IS NOT DISTINCT FROM:

<code class="language-sql">(a = b OR a IS NULL AND b IS NULL)</code>

These expressions account for NULL values. The IS DISTINCT FROM emulation ensures that if one operand is NULL, the result is TRUE unless both are NULL. The IS NOT DISTINCT FROM emulation simplifies to a direct equality check or a check for dual NULLs. This approach avoids the complexities of dealing with the UNKNOWN result that can arise from boolean logic involving NULLs.

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