MySQL 5.1 supports a row level replication. Before 5.1, it was a SQL statement replication, so that some functions such as UUID() were not replicated properly.

EXPLAIN (testing SQL);

MySQL does not use INDEX if you use LIKE '%...' or LIKE '_...'.
MySQL may not use INDEX if you use the result of some function.

SELECT * FROM table WHERE TO_DAYS(created_date) <= 7;

InnoDB's count(*) is much slower than MyISAM