* shimak
> How to use foreign key in mysql.
> I am using mysql 3.23.36
Just do it... :)
A foreign key is a field in a table referencing the primary key of another
table. In mysql you don't need to specify which columns are foreign keys,
you just use them in a join, and mysql will do the rest. Consider this basic
schema:
Person: id int, name varchar(30)
Phone: phone varchar(15),person int
The Person table contains person, each person have an unique id, defined as
the primary key.
The Phone table contains phone numbers. The phone column is the primary key
for the Phone table, two different persons can not have the same phone
number in this schema, but some persons may have multiple phone numbers.
The person column of the Phone table is an integer, and in this imaginary
application, this is used as a foreign key to the Person table. Mysql does
not need to know this, it is resolved when we do a query:
SELECT name,phone
FROM Person,Phone
WHERE
name LIKE "Baklund%" AND
Phone.person = Person.id;
The final row of this query takes care of the foreign key relationship.
<URL: http://www.mysql.com/doc/J/O/JOIN.html >
I should also mention the consept of forreign key constraints, the
possibility to tell mysql which column is a foreign key to which table, and
to make mysql enforce the integrity of the relationship. This is rather new
in mysql, available from version 3.23.43b.
<URL: http://www.mysql.com/doc/S/E/SEC445.html >
--
Roger
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