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  1. #1
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    I dont quite understand the user of primary key

    What primary keys are used for? I know that if I want to create index, I can use index keyword. I have keywords for creating unique and autoincrementing columns. It seems that I can do everithing what I need with other keywords. So can anybody explain why I need to use primary keys and in what situations?

  2. #2
    SQL Consultant gold trophysilver trophybronze trophy
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    for relating another table to this table with a foreign key
    rudy.ca | @rudydotca
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  3. #3
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    But I can join two tables without primary key using 'where' statement. I can use ANY column.

  4. #4
    SQL Consultant gold trophysilver trophybronze trophy
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    yes, you can join on whatever you want

    primary and foreign keys are used to ensure relational integrity

    this is often a new concept to mysql programmers, because mysql doesn't support relational integrity unless you use innodb tables
    rudy.ca | @rudydotca
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