Hello,
The index you have created is just fine and should be utilized as long as you perform
a query that needs to use an index.
Your query:
select a,b from t;
doesn't have any conditions imposed upon the table's rows. It just asks for all the
them. Simple file scan.
regards,
thalis
On Mon, 30 Apr 2001, Wix,Christian XCW wrote:
> Hi!
> I have some troubles with my index.
> I want to be able to use an index (test=(mintid, name)). I will use the
> index when I write: select mintid, name from loeb;
> I have created an index but it doesn't seem to work. Why?
> // Chris - Copenhagen
>
> mysql> show index from loeb;
> +-------+------------+----------+--------------+-------------+-----------+--
> -----------+----------+
> | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation |
> Cardinality | Sub_part |
> +-------+------------+----------+--------------+-------------+-----------+--
> -----------+----------+
> | loeb | 0 | PRIMARY | 1 | id | A |
> 90 | NULL |
> | loeb | 1 | rekord | 1 | mintid | A |
> NULL | NULL |
> | loeb | 1 | test | 1 | mintid | A |
> NULL | NULL |
> | loeb | 1 | test | 2 | name | A |
> NULL | NULL |
> +-------+------------+----------+--------------+-------------+-----------+--
> -----------+----------+
> 4 rows in set (0.00 sec)
>
> mysql> show columns from loeb;
> +----------+-------------+------+-----+----------+----------------+
> | Field | Type | Null | Key | Default | Extra |
> +----------+-------------+------+-----+----------+----------------+
> | name | varchar(20) | | | | |
> | distance | double(3,1) | | | 0.0 | |
> | dato | date | YES | | NULL | |
> | id | int(11) | | PRI | 0 | auto_increment |
> | tottid | time | | | 00:00:00 | |
> | mintid | time | | MUL | 00:00:00 | |
> | art | varchar(10) | YES | | NULL | |
> +----------+-------------+------+-----+----------+----------------+
> 7 rows in set (0.00 sec)
>
> mysql> explain select mintid, name from loeb;
> +-------+------+---------------+------+---------+------+------+-------+
> | table | type | possible_keys | key | key_len | ref | rows | Extra |
> +-------+------+---------------+------+---------+------+------+-------+
> | loeb | ALL | NULL | NULL | NULL | NULL | 90 | |
> +-------+------+---------------+------+---------+------+------+-------+
> 1 row in set (0.00 sec)
>
>
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