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".
Example of Table Literal - SQL Example: A Table Literal (correct version) VALUES ('S1', 'C1', 'Anne'), ('S1', 'C2', 'Anne'), ('S2', 'C1', 'Boris'), ('S3', 'C3'
Table Literals - SQL One might expect SQL to support table literals in the manner illustrated in Example 2.2, but in fact that is not a legal SQL expression. Example: Not a
SELECT INTO Statement The SELECT INTO statement retrieve data from one or more database tables, and then assigns the selected values to the variables or fields. Syntax:
Opening a Cursor Variable The OPEN-FOR statement relates a cursor variable with the multi-row query, executes the query, and then identifies the result set. The syntax for ope
Using DEFAULT You can use the keyword DEFAULT rather than that of the assignment operator to initialize the variables. For e.g. the declaration blood_type CHAR := ’O’; it can b
COMMIT Statement The COMMIT statement explicitly makes everlasting changes to the database during the present transaction. The Changes made to the database are not considered e
Using Operator REF: You can retrieve refs by using the operator REF that, like VALUE, takes as its argument a correlation variable. In the illustration below, you retrieve one
Assignment Source Not a Literal - Variable Syntax: SET SN = SID (SUBSTRING (SN.C FROM 1 FOR 1)||'5');
ROWID The ROWID returns the rowid (binary address) of a row in the database table. You can use the variables of the type UROWID to store rowids in a readable format. In the il
Subprograms The PL/SQL has two types of subprograms known as the procedures and functions that can take parameters and be invoked. As the following example represents, a subp
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