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SQL :: What are primary keys and foreign keys?

posted Sep 13, 2012, 3:09 AM by Ashish Jain
Primary keys are the unique identifiers for each row. They must contain unique values and cannot be null. Due to their importance in relational databases, Primary keys are the most fundamental of all keys and constraints. A table can have only one Primary key.
Foreign keys are both a method of ensuring data integrity and a manifestation of the relationship between tables.