"not enforced" table constraints - sql, PL-SQL Programming

Assignment Help:

"Not Enforced" Table Constraints

A constraint that is not enforced is not really a constraint within the meaning of the act, but SQL does have such a concept and it needs to be mentioned here. With the exception of UNIQUE and PRIMARY KEY specifications, a table constraint can be declared as either ENFORCED (the default option) or NOT ENFORCED. The "enforcement characteristic" of such a constraint can be changed by means of an ALTER TABLE statement. For example, the table constraint MAX_ENROLMENTS becomes not enforced by execution of the statement ALTER TABLE ALTER CONSTRAINT MAX_ENROLMENTS NOT ENFORCED. The immediate effect is the same (ignoring effects on the catalog) as if ALTER TABLE DROP CONSTRAINT MAX_ENROLMENTS had been given. However, it's easier to reinstate the constraint using ALTER TABLE ALTER CONSTRAINT MAX_ENROLMENTS ENFORCED. NOT ENFORCED cannot be specified for domain constraints or assertions, so use of CREATE ASSERTION should really be the preferred method of declaring a constraint, but unfortunately that option is not widely available.


Related Discussions:- "not enforced" table constraints - sql

Effects of null in aggregate operator - sql, Effects of NULL in Aggregate O...

Effects of NULL in Aggregate Operator - SQL Let aggop(x) be an invocation of some aggregate operator aggop in SQL, where x is an expression (usually an open expression) to be

Calculate the number of tuples, Question: (a) The objective of query opti...

Question: (a) The objective of query optimization is to choose the most efficient strategy for implementing a given relational query, thereby improving the system performance. On

Identifiers in pl/sql, Identifiers You use identifiers to name the PL/S...

Identifiers You use identifiers to name the PL/SQL program items and units that include constants, variables, cursors, exceptions, cursor variables, subprograms, and packages.

In operator-comparison operators, IN Operator The operator IN tests the ...

IN Operator The operator IN tests the set membership. This means "equal to any member of." The set may have nulls, but they are ignored. For illustration, the statement below do

Order of evaluation-pl/sql expressions , Order of Evaluation When you do...

Order of Evaluation When you do not use the parentheses to specify the order of evaluation, the operator precedence determine the order. Now compare the expressions below: NOT

Parameter and keyword description - packages, Parameter and Keyword Descrip...

Parameter and Keyword Description: package_name: This construct identifies the package. AUTHID Clause: This determine whether all the packaged subprograms impleme

Exceptions - syntax, Exceptions An exception is the runtime error or wa...

Exceptions An exception is the runtime error or warning condition that can be predefined or user-defined. The Predefined exceptions are raised implicitly through runtime system

Cursors in pl/sql, Cursors The Oracle uses work areas to execute the SQ...

Cursors The Oracle uses work areas to execute the SQL statements and to store process information. A PL/SQL construct known as the cursor. Let's you assume name a work area and

Using for update, Using FOR UPDATE If you declare a cursor which will ...

Using FOR UPDATE If you declare a cursor which will be referenced in the CURRENT OF clause of an UPDATE or DELETE statement, you should use the FOR UPDATE clause to obtain an

Data types in sql - character, Data Types in SQL - Character CHARACTER...

Data Types in SQL - Character CHARACTER or, synonymously, CHAR, for character strings. When this type is to be the declared type of something (e.g., a column), the permissible

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

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!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd