Primary key and foreign key differentiation

[Smita.bendal]

Hi Guys ,

I am just started to learn the SQL . You know there are various keys like primary fey, unique key are used in the SQL. I have little-bit knowledge about the primary key but don't know in detail.

Is anybody know about "Primary key and foreign key differentiation" ?

[Praetor]

Hi friends,

1. In a single table there is only foreign key you can use . On other hand you can use more than one foreign keys in a single table.

2. Primary key from one table is the foreign key for the another table. Primary key is must not be repeated in the same table.

2.You can not assign "null value" to the primary key of the table.

[Katty]

Following are some differentiation between Primary key and foreign key:

1. A primary key is a field value or combination of fields values which is useful to identify a record from the table uniquely.

2. The advantage of the foreign key is that it enables the methods for referencing other table through the primary key of that table.

3. You are able to locate individual record through the "Primary key". "Foreign key" is works as referencing key for the different tables

4. "Primary key" don't have any duplicate value for the field ,while "Foreign key" may have duplicate value for the same field.

[kelfro]

Hi Friend,

Please go through the below some information regarding Primary key and foreign key:

*. Primary key is useful in identifying a row of the table as well as it doesn't comprises "null values". And this property of the Primary key is useful to prevent rows duplication.

*. Foreign key is useful in identifying a column of the table and can comprises "null values"

*. In the Relational database concepts , a foreign key works as a
referential constraint among the two different tables.