Syntax
NVL(str1,replace_with)
Purpose
NVL() replaces NULL with the specified value. If the value of str1 is NULL, the value specified by replace_with is returned. str1 is generally a column name. replace_with can be a literal (for example, a hard-coded value), a reference to another column, or an expression.
This replacement improves the output.
Examples
obclient> SELECT NVL(NULL, 0), NVL(NULL, 'a');
+--------------+----------------+
| NVL(NULL, 0) | NVL(NULL, 'a') |
+--------------+----------------+
| 0 | a |
+--------------+----------------+
1 row in set
