Already have an account? Get multiple benefits of using own account!
Login in your account..!
Remember me
Don't have an account? Create your account in less than a minutes,
Forgot password? how can I recover my password now!
Enter right registered email to receive password!
Procedural Constraint Enforcement (Triggers)
SQL has an alternative method of addressing database integrity, involving event-driven procedural code. The special procedures that can be used for this purpose are called triggers and the events that activate them are specified update operations. For example, suppose it is required for every row in IS_CALLED to have a matching row on StudentId in IS_ENROLLED_ON, enforcing a business rule to the effect that every registered student must be enrolled on at least one course. Then a triggered procedure might be activated every time INSERT is used to add a row to IS_CALLED, checking to see if a matching row exists in IS_ENROLLED_ON and raising an exception if there isn't one. But that wouldn't be sufficient to address the requirement.
Further triggers would be needed, activated by UPDATE statements on IS_CALLED and IS_ENROLLED_ON that cause changes to StudentId values in either of those tables, and by DELETE statements on IS_ENROLLED_ON. As this simple example demonstrates, use of triggered procedures for constraint enforcement can be complicated and error-prone. As one practitioner told me, "It quickly gets so complicated that it's almost impossible for a human not to make errors..., and even when you're not facing a 'complicated' case, the work to be done is tedious and boring".
Keyword and Parameter Description select_statement: This is a query which returns a result set of the rows. Its syntax is such that of select_ into_statement without the IN
Block Structure The PL/SQL is a block-structured language. That is, the fundamental units (procedures, anonymous blocks, and functions) that make up a PL/SQL program are logi
Declaring a Cursor The Forward references are not allowed in the PL/SQL. Therefore, you must declare a cursor before referencing it in other statements. Whenever you declare a
Interesting properties of CROSS JOIN - SQL Compare these with the "interesting properties of JOIN", CROSS JOIN is associative but not commutative. Unlike JOIN and NATURAL JOI
DELETE Command - SQL Loosely speaking, DELETE removes some existing rows from its target table. Suppose the university decides that course C3 is to be withdrawn. Example shows
PITS Depressions in secondary cell wall is called pit. A pit present on the free cell wall surface without its partner is called Blind pit. It consists of 2 parts -
%ROWCOUNT The %ROWCOUNT yields the number of rows affected by the INSERT, UPDATE, or DELETE statement, or returned by a SELECT INTO statement. The %ROWCOUNT yields zero when a
Running the PL/SQL Wrapper To run the PL/SQL Wrapper, go through the wrap command at your operating system prompt by using the syntax as shown: wrap iname=input_file [oname=
Project Description: I am looking to change FullCalendar to add/delete sql server data when events are removed or dropped from Calendar. Events should only be included by dra
Use the RETURNING Clause Frequently, the application requires information about the row affected by a SQL operation, for illustration, to produce a report or take a subsequent
Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!
whatsapp: +91-977-207-8620
Phone: +91-977-207-8620
Email: [email protected]
All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd