Returns a substitute value when a value is NULL.
NVL(expr1, expr2)
NVL returns a substitute value when the specified value is NULL. When expr1 is NULL, expr2 is returned. When expr1 is not NULL, expr1 is returned.
Specify the same data types for expr1 and expr2. However, if a constant is specified in expr2, and the data type can also be converted by expr1, different data types can be specified. When this happens, the conversion by expr2 is done to suit the data type in expr1, so the value of expr2 returned when expr1 is a NULL value will be the value converted in the data type of expr1.
When specifying literals, refer to "Table A.1 Data type combinations that contain literals and can be converted implicitly" in "A.3 Implicit Data Type Conversions" for information on the data types that can be converted.
Example
In the following example, "IS NULL" is returned if the value of col1 in table t1 is a NULL value.
SELECT col2, NVL(col1,'IS NULL') "nvl" FROM t1; col2 | nvl ------+--------- aaa | IS NULL (1 row)
