Форум пользователей MySQL

mysql> create table t_7091(id int);
Query OK, 0 rows affected (0.27 sec)

mysql> insert into t_7091(id) values(1),(2),(3),(5),(6),(8);
Query OK, 6 rows affected (0.00 sec)
Records: 6  Duplicates: 0  Warnings: 0

mysql> select id from (SELECT t.*,@rownum := @rownum + 1 AS rank FROM t_7091 t,(SELECT @rownum := 0) r) t1 where rank%2=0;
+------+
| id   |
+------+
|    2 |
|    5 |
|    8 |
+------+
3 rows in set (0.00 sec)

mysql>  SET @i = 0; SELECT id FROM (SELECT @i := @i + 1 AS i, id FROM t_7091) a WHERE a.i%2=0;
Query OK, 0 rows affected (0.00 sec)

+------+------+
| i    | id   |
+------+------+
|    2 |    2 |
|    4 |    5 |
|    6 |    8 |
+------+------+
3 rows in set (0.00 sec)