哪两个查询会更快？

Question

SELECT * FROM table WHERE col IN (1,2,3)

要么

SELECT * FROM table WHERE col = 1 OR col = 2 OR col = 3

Answer 1

他们是一样的.

编辑:它们在MySQL中是相同的.

使用索引:

mysql> explain select * from trees where id = 1 or id = 2;
+----+-------------+-------+-------+---------------+---------+---------+------+------+-------------+
| id | select_type | table | type  | possible_keys | key     | key_len | ref  | rows | Extra       |
+----+-------------+-------+-------+---------------+---------+---------+------+------+-------------+
|  1 | SIMPLE      | trees | range | PRIMARY       | PRIMARY | 8       | NULL |    2 | Using where |
+----+-------------+-------+-------+---------------+---------+---------+------+------+-------------+

mysql> explain select * from trees where id in (1,2);
+----+-------------+-------+-------+---------------+---------+---------+------+------+-------------+
| id | select_type | table | type  | possible_keys | key     | key_len | ref  | rows | Extra       |
+----+-------------+-------+-------+---------------+---------+---------+------+------+-------------+
|  1 | SIMPLE      | trees | range | PRIMARY       | PRIMARY | 8       | NULL |    2 | Using where |
+----+-------------+-------+-------+---------------+---------+---------+------+------+-------------+

使用全表扫描:

mysql> explain select * from trees where version = 1 or version = 2;
+----+-------------+-------+------+---------------+------+---------+------+------+-------------+
| id | select_type | table | type | possible_keys | key  | key_len | ref  | rows | Extra       |
+----+-------------+-------+------+---------------+------+---------+------+------+-------------+
|  1 | SIMPLE      | trees | ALL  | NULL          | NULL | NULL    | NULL |    7 | Using where |
+----+-------------+-------+------+---------------+------+---------+------+------+-------------+

mysql> explain select * from trees where version in (1,2);
+----+-------------+-------+------+---------------+------+---------+------+------+-------------+
| id | select_type | table | type | possible_keys | key  | key_len | ref  | rows | Extra       |
+----+-------------+-------+------+---------------+------+---------+------+------+-------------+
|  1 | SIMPLE      | trees | ALL  | NULL          | NULL | NULL    | NULL |    7 | Using where |
+----+-------------+-------+------+---------------+------+---------+------+------+-------------+