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NULLIF function

Returns NULL if two expressions are equal; otherwise, returns the first expression.

Syntax

NULLIF(expression1, expression2)

Arguments

  • expression1: The first expression.

  • expression2: The expression to compare against.

Returns

  • Returns NULL if expression1 equals expression2.

  • Returns expression1 if the expressions are not equal.

  • The return type matches the type of expression1.

Examples

-- Example 1: Equal values return NULL
> SELECT NULLIF(5, 5);
NULL

-- Example 2: Different values return first expression
> SELECT NULLIF(5, 10);
5

-- Example 3: String comparison
> SELECT NULLIF('hello', 'hello');
NULL

> SELECT NULLIF('hello', 'world');
'hello'

Notes

NULLIF(a, b) is equivalent to: sql CASE WHEN a = b THEN NULL ELSE a END

See Also