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What is Trigger?
A trigger is a SQL procedure that initiates an action when an event (INSERT, DELETE or UPDATE) occurs. Triggers are kept in and managed by the DBMS. Triggers are used to maintain the referential integrity of data by changing the data in a systematic fashion. A trigger cannot be called or implemented; DBMS automatically fires the trigger as a result of a data modification to the associated table. Triggers can be viewed as same to stored procedures in that both having of procedural logic that is kept at the database level. Stored procedures, though, are not event-drive and are not attached to a specific table as triggers are. Stored procedures are explicitly implemented by invoking a CALL to the procedure whereas triggers are implicitly executed. In addition, triggers can also execute stored procedures.
Sub query in the UPDATE command : Example : //Double the commission for employees, who have got at least 2 increments. UPDATE EMP SET COMM = COMM * 2 WHERE
1. Determine that the Checkpoints are a part of Ans: Checkpoints are a part of Recovery measures
Oracle & Distributed Databases 1. Differentiate between PL/SQL functions and procedures. 2. Draw the diagram of logical structure of oracle database and explain it in brief.
Differentiate between a subquery and a join If we need to acquire information from one or more tables after that either subquery or join can be used. If the columns which are t
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How does Tuple-oriented relational calculus vary from domain-oriented relational calculus? The tuple-oriented calculus uses a tuple variables i.e., variable whose only allowed
Implementation and SQL Applications
What is trigger? Triggers are statements that are executed automatically by the system as the side effect of a modification to the database.
Database Errors: An error is said to have occurred if the implementation of a command to manipulate the database cannot be successfully finished either due to inconsistent data or
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