Question

Is there a difference between the following two statements:

mysql> EXPLAIN SELECT IF(arms IS NULL, 'asdf', arms) FROM limbs;
+----+-------------+-------+------+---------------+------+---------+------+------+-------+
| id | select_type | table | type | possible_keys | key  | key_len | ref  | rows | Extra |
+----+-------------+-------+------+---------------+------+---------+------+------+-------+
|  1 | SIMPLE      | limbs | ALL  | NULL          | NULL | NULL    | NULL |   12 |       |
+----+-------------+-------+------+---------------+------+---------+------+------+-------+
1 row in set (0.00 sec)

mysql> EXPLAIN SELECT IF(arms IS NULL, 'asdf', arms) FROM limbs;
+----+-------------+-------+------+---------------+------+---------+------+------+-------+
| id | select_type | table | type | possible_keys | key  | key_len | ref  | rows | Extra |
+----+-------------+-------+------+---------------+------+---------+------+------+-------+
|  1 | SIMPLE      | limbs | ALL  | NULL          | NULL | NULL    | NULL |   12 |       |
+----+-------------+-------+------+---------------+------+---------+------+------+-------+
1 row in set (0.00 sec)

Does one perform better or is preferable over the other? Or are they identical?

Answer 1

IFNULL is just a syntactic sugar for IF, which is a syntactic sugar for ANSI SQL CASE.

So use whichever you like better and whichever fits your particular needs.

PS: EXPLAIN doesn’t rely on SELECT