Question

I have very strange problem with mySQL and simple query with simple index. I am trying to use this query:

SELECT * FROM `counter_links` WHERE `link_id`=1544;

as you can see there is also index named link_id:

mysql> show indexes from counter_links;
+---------------+------------+-------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+----------+---------------+
| Table         | Non_unique | Key_name    | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment  | Index_comment |
+---------------+------------+-------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+----------+---------------+
| counter_links |          1 | link_id     |            1 | link_id     | A         |        NULL |     NULL | NULL   |      | BTREE      | disabled |               |
+---------------+------------+-------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+----------+---------------+
1 row in set (0.12 sec)

But look what EXPLAIN returned:

mysql> explain SELECT * FROM `counter_links` WHERE `link_id`=1544;
+----+-------------+---------------+------+---------------+------+---------+------+----------+-------------+
| id | select_type | table         | type | possible_keys | key  | key_len | ref  | rows     | Extra       |
+----+-------------+---------------+------+---------------+------+---------+------+----------+-------------+
|  1 | SIMPLE      | counter_links | ALL  | NULL          | NULL | NULL    | NULL | 22103687 | Using where |
+----+-------------+---------------+------+---------------+------+---------+------+----------+-------------+
1 row in set (0.03 sec)

Why mySQL don’t use index there? I see that the same is working good on smaller version of the table, but I am not able to recognize where the problem is. You do?

It is more stranger that it seems, because lower IDs sometimes works with the index.

Thanks you for all comments in advance!

Cheers!

Jakub

Answer 1

The comment field for th eindex says that the index is disabled, not sure why.

ALTER TABLE … ENABLE KEYS may work