There are two different methods of retrieving the list of Primary Keys and Foreign Keys from database.
Method 1: INFORMATION_SCHEMA
SELECT DISTINCT Constraint_Name AS [Constraint], Table_Schema AS [Schema], Table_Name AS [TableName] FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE GO
Method 2: sys.objects
SELECT OBJECT_NAME(OBJECT_ID) AS NameofConstraint, SCHEMA_NAME(schema_id) AS SchemaName, OBJECT_NAME(parent_object_id) AS TableName, type_desc AS ConstraintType FROM sys.objects WHERE type_desc IN ('FOREIGN_KEY_CONSTRAINT','PRIMARY_KEY_CONSTRAINT') GO
I am often asked about my preferred method of retrieving list of Primary Keys and Foreign Keys from database. I have a standard answer. I prefer method 2, which is querying sys database. The reason is very simple. sys. schema always provides more information and all the data can be retrieved in our preferred fashion with the preferred filter.
Let us look at the example we have on our hand. When Information Schema is used, we will not be able to discern between primary key and foreign key; we will have both the keys together. In the case of sys schema, we can query the data in our preferred way and can join this table to another table, which can retrieve additional data from the same.
Let us play a small puzzle here. Try to modify both the scripts in such a way that we are able to see the original definition of the key, that is, create a statement for this primary key and foreign key.
If I get an appropriate answer from my readers, I will publish the solution on this blog with due credit.
Reference : Pinal Dave (http://blog.SQLAuthority.com)