Constraints are one of the fundamental concepts, which arrive at a very elementary stage of Database designing. Constraints are nothing but the rules on the data. This preserves the Entity integrity, Referential Integrity, and Domain Integrity of the data. While entity integrity focusses on uniqueness and NULLable property of a data, referential checks the data of a column ‘in reference to’ its parent column. Domain integrity defines a domain set for a column.
They are imposed upon the table columns, where they act as barrier for the incoming data. Once the checks are activated, only the obedient data is allowed to grab the seat. System raises the ‘Violating’ exception, if the data fails the constraint rule.
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