NULLIF (SQL)
Synopsis
NULLIF(expression1,expression2)
Description
The NULLIF function returns NULL if the value of expression1 is equal to the value of expression2. Otherwise, it returns the expression1 value.
NULLIF is equivalent to:
SELECT CASE
WHEN value1 = value2 THEN NULL
ELSE value1
END
FROM MyTableCollations are applied to expression1 and expression2 before they are compared for equality. If they are not equal, the resulting expression has the collation of expression1.
Arguments
expression1
An expression, which can be the name of a column, a numeric or string literal, a host variable, or the result of another scalar function.
expression2
An expression, which can be the name of a column, a numeric or string literal, a host variable, or the result of another scalar function.
NULLIF returns the same data type as expression1.
NULL Handling Functions Compared
The following table shows the various SQL comparison functions. Each function returns one value if the logical comparison tests True (A same as B) and another value if the logical comparison tests False (A not same as B). These functions allow you to perform NULL logical comparisons. You cannot specify NULL in an actual equality (or non-equality) condition comparison.
| SQL Function | Comparison Test | Return Value |
|---|---|---|
| NULLIF(ex1,ex2) | ex1 = ex2 |
True returns NULL False returns ex1 |
| ISNULL(ex1,ex2) | ex1 = NULL |
True returns ex2 False returns ex1 |
| IFNULL(ex1,ex2) [two-argument form] | ex1 = NULL |
True returns ex2 False returns NULL |
| IFNULL(ex1,ex2,ex3) [three-argument form] | ex1 = NULL |
True returns ex2 False returns ex3 |
| {fn IFNULL(ex1,ex2)} | ex1 = NULL |
True returns ex2 False returns ex1 |
| NVL(ex1,ex2) | ex1 = NULL |
True returns ex2 False returns ex1 |
| COALESCE(ex1,ex2,...) | ex = NULL for each argument |
True tests next ex argument. If all ex arguments are True (NULL), returns NULL. False returns ex |
Examples
The following example uses the NULLIF function to set to null the display field of all records with Age=20:
SELECT Name,Age,NULLIF(Age,20) AS Nulled20
FROM Sample.Person
