Question

I use MySQL server version 5.5.14 and now I am trying this simple SQL query with Explain command:

EXPLAIN SELECT id, name, thumb FROM `twitter_profiles` LIMIT 10;

and it shows me this result:

+----+-------------+-------+------+---------------+------+---------+------+-------+-------+
| id | select_type | table | type | possible_keys | key  | key_len | ref  | rows  | Extra |
+----+-------------+-------+------+---------------+------+---------+------+-------+-------+
|  1 | SIMPLE      | tp    | ALL  | NULL          | NULL | NULL    | NULL | 40823 |       |
+----+-------------+-------+------+---------------+------+---------+------+-------+-------+
1 row in set (0.02 sec)

My question is why it scans whole table instead of taking the first 10 rows as I specified in LIMIT clause?

Answer 1

here a good link of article about MySQL EXPLAIN limits and errors

LIMIT is not taken into account while estimating number of rows Even
if you have LIMIT which restricts how many rows will be examined MySQL
will still print full number