viewnotes/2163/DME 101 Management Principles and Values

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Discuss the significance of assertion? Database Management Systems - 10CS54 VTU notes (DEC/JAN 2013/ JAN- 2014)

Write an assertion to specify constraint such that the salary of an employee must not be greater than the salary of the manager of the department that employees works for?


By:anonymousguy7799

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CREATE ASSERTION SALARY_CONSTRAINTCHECK (NOT EXISTS (SELECT *FROM EMPLOYEE E, EMPLOYEE M, DEPARTMENT DWHERE E.SALARY > M.SALARY ANDE.DNO=D.NUMBER AND D.MGRSSN=M.SSN))
An assertion is a piece of SQL which makes sure a condition is satisfied or it stops action being taken on a database object. It could mean locking out the whole table or even the whole database. 
To make matters more confusing - a trigger could be used to enforce a check constraint and in some DBs can take the place of an assertion (by allowing you to run code un-related to the table being modified). 
A common mistake for beginners is to use a check constraint when a trigger is required or a trigger when a check constraint is required.

Nikhil-bharadwaj

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