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Describe integrity constraints?
Integrity Constraints - A database is just as excellent as the information stored in it, and a DBMS must therefore help avoid the entry of incorrect information. An integrity constraint is a condition specified on a database schema and restricts the data that can be stored in an instance of the database. If a database instance satisfies all the integrity constraints specified on the database schema, it is a legal instance. A DBMS enforces integrity constraints, in that it permits only legal instances to be stored within the database.
Integrity constraints are specified and enforced at various times:
When the DBA or end user describes a database schema, he or she specifies the integrity constraints which must carry on any instance of this database. While a database application is run, the DBMS checks for violations and disallows changes to the data in which violate the specified integrity constraints. Several types of integrity constraints can be specified in the relational model, such as, Not Null, Check, Unique, Primary Key, etc.
Improved performance: As the data is located near the site of its demand, and given the inherent parallelism because of multiple copies, speed of database access may be good for di
Why 'AS' clause is used in SQL ? 'As' clause is used for Rename operation. ‘AS' clause is used in SQL for rename operation. (e.g., SELECT ENO AS EMPLOYEE_NO FROM EMP)
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If the insertion violates one or more constraints, then two alternatives are available: Default option: - Insertion can be discarded and the reason of refusal can also be ex
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