Primary and Foreign Keys

Primary Key is also known as Pkey, and Foreign Key is also known as Fkey. These are one of the most important terms without which a proper Data Model cannot be created.

We have understood what a table is. Now, the next step is to understand, if there is more than one table then how to join both. In the topic ‘Tables, Columns and Rows’ we used an example of table ‘Family’. Let’s use the same table here with an additional column i.e., Birth Location.

Table Name: Family

Now let’s say, to save space in Family table as we can see ‘United State of America’ has been used many times so how about creating another table where let’s store lengthy country names and in Family tables, let use country code instead with there is another table called as Birth Location.

Table Name: Birth Location

Now, let’s update the Family table to reflect country code instead of country name.

Table Name: Family

Now, the problem is column ‘Birth Location’ have country code so how to find out which country name refer to ‘001’. Let’s declare ID in Birth_Location table as Pkey and Location_ID in Family table as Fkey.

Table Name: Birth_Location

Table Name: Family

Now, we can join both tables using Primary and Foreign Key columns and can extract the relevant full country names.