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Difference between primary key and unique key A table can have only one primary key but multiple unique keys. unique key may have null value which is not allowed in primary. simply primary key is unique + not null where as unique key Field contains any number of NULL values. Find primary key, index_name ,index key  using sp_Help command in sql How to find primary key, index_name and index_key in the same query For a particular table and also want to group by index_name use sysindexes table to get the output you want use the stored procedure sp_helpindex [object name] sp_help 'table name' Null and Not Null value in Primary and unique keys in sql Primary key should contain unique value and not null because if attribute value is null than how should maintain the uniqueness.. one more think i want to add that Primary key is a type of constraint and foreign key is also a type of constraint and pk is null then u can't use the null value as a foreign key. S...