December 15, 2014 at 6:53 pm
What is the simple way to remember Primary and foreign key?
Why is the ID column in a table declared as a integer datatype?
December 15, 2014 at 10:43 pm
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December 16, 2014 at 5:03 am
Just to know what they are.
The primary key uniquely identifies a row.
A foreign key is used to relate one table to another. It uses the primary key (or any other unique constraint) to make this relationship.
This means that the foreign key in most tables is dependent on the primary key. Because of this, you can think of the primary key as coming first. Create a primary key and then you can create foreign keys on other tables to relate to the table you just created a primary key on.
An IDENTITY doesn't have to be on an integer, but, as you can read in the definition, it's an increasing number. So, it has to be on a number field, but it's very nature. It's a number, so it has to be stored as a number.
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