NVL is a function in SQL that is used to replace null values with a specified value. It is defined only in Oracle, not in SQL Server or MySQL. The syntax of the NVL function is NVL(expr1, expr2), where expr1 is the source value or expression that may contain a null, and expr2 is the target value for converting the null. If expr1 is null, then NVL returns expr2. If expr1 is not null, then NVL returns expr1 . NVL can be used with any data type, including date, character, and number.