mysql> EXPLAIN SELECT EXISTS(SELECT 1 FROM xbl WHERE xuid LIKE '%25%' ORDER BY xuid DESC LIMIT 5000);
+----+-------------+-------+------------+-------+---------------+------+---------+------+-------+----------+--------------------------+
| id | select_type | table | partitions | type  | possible_keys | key  | key_len | ref  | rows  | filtered | Extra                    |
+----+-------------+-------+------------+-------+---------------+------+---------+------+-------+----------+--------------------------+
|  1 | PRIMARY     | NULL  | NULL       | NULL  | NULL          | NULL | NULL    | NULL |  NULL |     NULL | No tables used           |
|  2 | SUBQUERY    | xbl   | NULL       | index | NULL          | xuid | 8       | NULL | 37458 |    11.11 | Using where; Using index |
+----+-------------+-------+------------+-------+---------------+------+---------+------+-------+----------+--------------------------+
2 rows in set, 1 warning (0.00 sec)

mysql> SELECT COUNT(1) FROM xbl;
+----------+
| COUNT(1) |
+----------+
|    38725 |
+----------+
1 row in set (0.00 sec)