Anna Winkler wrote:
>
> When I create a key or index, the value shown in the key field is MUL.
> What does MUL mean? Is there any way to determine if the field is a key
> or index?
>
> I created a test table with:
>
> mysql> create table key_test (key1 char(10) not null, key2 char(5) not null,
> index1 int not null, field4 char(12) not null, primary key (key1), key (key2), index
> (index1), unique (field4));
> Query OK, 0 rows affected (0.01 sec)
>
> So then I have this table:
>
> mysql> describe key_test;
> +--------+----------+------+-----+---------+-------+
> | Field | Type | Null | Key | Default | Extra |
> +--------+----------+------+-----+---------+-------+
> | key1 | char(10) | | PRI | | |
> | key2 | char(5) | | MUL | | |
> | index1 | int(11) | | MUL | 0 | |
> | field4 | char(12) | | UNI | | |
> +--------+----------+------+-----+---------+-------+
>
> I tried a show index:
>
> mysql> show index from key_test;
>
> +----------+------------+----------+--------------+-------------+-----------+-------------+----------+
> | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation |
> Cardinality | Sub_part |
>
> +----------+------------+----------+--------------+-------------+-----------+-------------+----------+
> | key_test | 0 | PRIMARY | 1 | key1 | A |
> 0 | NULL |
> | key_test | 1 | key2 | 1 | key2 | A |
> NULL | NULL |
> | key_test | 1 | index1 | 1 | index1 | A |
> NULL | NULL |
> | key_test | 0 | field4 | 1 | field4 | A |
> 0 | NULL |
>
> +----------+------------+----------+--------------+-------------+-----------+-------------+----------+
> 4 rows in set (0.00 sec)
>
> But it still isn't clear to me how I know key2 is a KEY and index1 is an INDEX?
>
> Thanks for your help,
> Anna Winkler
>
You can think of INDEX as being synonymous with KEY for the purpose of
simplicity.
A field is really never an index, but it can be a part of an index. Very
often an index consist of only one field, and we call that field a key,
although strictly speaking this is not correct - we should say that we
have a key consisting of the field.
MUL means that the field is a part of an index that has other fields.
--
Sasha Pachev
http://www.sashanet.com
