Primary Key vs Foreign Key

2 Answers

1. 
   

   
   

   muneendra vemula on Feb 24, 2014 Reply

   Primary key does not allow duplicates.
   And Foreign key references the primary key field.

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2. 
   

   
   

   lilsam on Jul 14, 2016 Reply

   The concept of Primary and Foreign key relates to a common identity which binds different record data.

   It creates a Parent-Child relationship between different record data.
   Consider EMPLOYEE record which has EMPLID as PK and record DEPARTMENT which has DEPTID as PK as well as an additional key EMPLID which is also a key field.

   Suppose, we want to find out all the EMPLOYEES who are assigned to a DEPARTMENT, then we can make use of the EMPLID field present in both records. So, here the EMPLID from EMPLOYEE record acts a PK which will be joined to EMPLID of DEPARTMENT record which acts as a FK.

   SELECT A.EMPLID,B.DEPTID
   FROM EMPLOYEE A, DEPARTMENT B
   WHERE A.EMPLID = B.EMPLID

   Hope this is meaningful!

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