N/APosted on - 03/09/2012
Can anyone please explain to me what is Primary key and what is Foreign Key and the purpose of using this type of keys for databases
Primary key and Foreign Key
Primary key: It uniquely identifies every record in the relational table. It can either be a guaranteed normal attribute to be unique (such as SSS or Social Security Number in a table with no greater than one record/person) or it can be created by the DBMS (such as a globally unique identifier, in Microsoft SQL Server, or GUID). Primary keys might contain a single attribute or multiple attributes that are combined.
Let’s take for example we have a STUDENTS table that consists a record for every student at a university. It would be a great choice to use the student's unique ID number for a primary key in the STUDENTS table. The reason behind this is that the student's first and last name would not be a good choice, as sometimes two or more students have the same names which is very common.
Foreign Key: It is a field in a relational table that compares the primary key column of another table. In order to do cross-referencing of tables, you can use the foreign key. Establishing relationships between database tables is one of the most important concepts in databases. These provide a mechanism for linking data stored in different tables and retrieving it in an efficient way possible. In order to establish a link between two tables, you must specify a foreign key in one table that references a column from a different table.