gistfile1.txt

> create table t(a int, b int, primary key(a));
Query OK, 0 rows affected (0.23 sec)

> insert into t values (1,1),(2,2),(3,3),(4,4),(5,5),(6,6),(7,7),(8,8),(9,9),(10,10),
    -> (11,11),(12,12),(13,13),(14,14),(15,15),(16,16),(17,17),(18,18),(19,19),(20,20),
    -> (21,11),(22,12),(23,13),(24,14),(25,15),(26,16),(27,17),(28,18),(29,19),(30,30),
    -> (31,11),(32,12),(33,13),(34,14),(35,15),(36,16),(37,17),(38,18),(39,19),(40,40),
    -> (41,11),(42,12),(43,13),(44,14),(45,15),(46,16),(47,17),(48,18),(49,19),(50,50),
    -> (51,11),(52,12),(53,13),(54,14),(55,15),(56,16),(57,17),(58,18),(59,19),(60,60);
Query OK, 60 rows affected (0.17 sec)
Records: 60  Duplicates: 0  Warnings: 0

> set long_query_time = 0.0;
Query OK, 0 rows affected (0.16 sec)

> select * from t where b = 60 order by a desc limit 1;
+----+------+
| a  | b    |
+----+------+
| 60 |   60 |
+----+------+
1 row in set (0.16 sec)

> select * from t where b = 60 limit 1;
+----+------+
| a  | b    |
+----+------+
| 60 |   60 |
+----+------+
1 row in set (0.16 sec)

> select rows_sent, rows_examined, sql_text from mysql.slow_log;
+-----------+---------------+------------------------------------------------------+
| rows_sent | rows_examined | sql_text                                             |
+-----------+---------------+------------------------------------------------------+
|         0 |             0 | set long_query_time = 0.0                            |
|         1 |             1 | select * from t where b = 60 order by a desc limit 1 |
|         1 |            60 | select * from t where b = 60 limit 1                 |
+-----------+---------------+------------------------------------------------------+
3 rows in set (0.17 sec)