![]() Primary keys not only ensure that each row has a unique value for the primary key columns, they also ensure that no rows contain NULL values for that column. All primary keys can be used to uniquely identify a specific row. Primary keys and foreign keys are both types of database constraint within MySQL.Ī primary key is a special column or column that is guaranteed to be unique across rows within the same table. You can find information about creating tables with primary and foreign keys in some of our other MySQL guides. ) How to create tables with primary keys and foreign keys ![]() You can use the IF NOT EXISTS clause by inserting it in the command after the CREATE TABLE phrase but before the table name: However, the optional IF NOT EXISTS clause can be added to the creation statement to override this behavior. MySQL's default behavior is to raise an error if you try to create a table that already exists. How do you create tables only if they don't already exist? For instance, you could have a table constraint that checks that a DATE_OF_BIRTH is before DATE_OF_DEATH in a table.
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