mysql>
The COALESCE() function returns the first value in the list of arguments that is not NULL.
If all values are NULL, then NULL is returned.
mysql>
COALESCE( [{, }...])
mysql>
mysql> SELECT COALESCE(NULL, 2, NULL, 3);
+----------------------------+
| COALESCE(NULL, 2, NULL, 3) |
+----------------------------+
| 2 |
+----------------------------+
1 row in set (0.00 sec)
mysql>