We state in the book that once constraints have been speci?ed in the schema, it is the responsibility of the DBMS to make sure that they are not violated by the execution of any transactions. SQL allows the application to control when each constraint is checked. If a constraint is in immediate mode, it is checked immediately after the execution of any SQL statement in a transaction that might make it false. If it is in deferred mode, it is not checked until the transaction requests to commit. Give an example where it is necessary for a constraint to be in deferred mode.
What will be an ideal response?
Suppose the constraint states that the value of one attribute, A, is the sum of the values of two other attributes, B and C . If we want to increment the value of B,we must also increment the value of A in the same transaction. But no matter in what order we do the incrementing, the constraint will be false between the two statements that do the incrementing, and if we used immediate mode checking, the transaction would abort when the ?rst increment statement was attempted.
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When the call by reference using reference parameters technique is used for passing a variable's address to a function, what must be included in the call statement?
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What will be an ideal response?
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What will be an ideal response?