how do indices in mysql tables (MyISAM) work?

Posted by understack on Stack Overflow See other posts from Stack Overflow or by understack
Published on 2010-03-31T08:12:56Z Indexed on 2010/03/31 8:23 UTC
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Filed under:

mysql

|

indexing

|

primary-key

Few basic doubts I have:

1. Is primary key column automatically indexed?

2. What should be criteria to select index column?

3. When should I club multiple columns?

4. Does MyISAM or InnoDB has any affect on this?

5. Are they really required, specially in case if primary key column is automatically indexed?

Thanks.

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