that the cache is not used to answer the query.
You may use RESET QUERY CACHE to remove all queries from the cache and
then your next query should be slow again. Same effect if you change
the table, because this makes all cached queries invalid.
+----------+
| count(*) |
+----------+
| 0 |
+----------+
1 row in set (7.22 sec)
mysql> select count(*) from users where email = 'hello';
+----------+
| count(*) |
+----------+
| 0 |
+----------+
1 row in set (0.45 sec)
mysql> select count(*) from users where email = 'hello';
+----------+
| count(*) |
+----------+
| 0 |
+----------+
1 row in set (0.45 sec)
mysql> select SQL_NO_CACHE count(*) from users where email = 'hello';
+----------+
| count(*) |
+----------+
| 0 |
+----------+
1 row in set (0.43 sec)