Adding table constraints, PL-SQL Programming

Assignment Help:

Adding Table Constraints

ALTER TABLE ENROLMENT ADD CONSTRAINT NameNotNull

CHECK (Name IS NOT NULL) ;

ALTER TABLE ENROLMENT ADD CONSTRAINT PK_StudentId_CourseId

PRIMARY KEY (StudentId, CourseId) ;

  1. ALTER TABLE ENROLMENT specifies that the definition of base table ENROLMENT is to be modified in some way, such as adding or dropping a column, adding or dropping a constraint (among other things).
  2. ADD CONSTRAINT NameNotNull specifies that in fact a constraint is being added to the definition of ENROLMENT, and the name by which that constraint can subsequently be referred to is NameNotNull. For example, the name would be needed if the constraint were later to be dropped, or perhaps it could appear in an error message when an attempted update is rejected for violating that constraint. Similar comments apply to ADD CONSTRAINT PK_StudentId_CourseId.
  3. CHECK (Name IS NOT NULL) specifies a truth-valued expression, Name IS NOT NULL, that must be satisfied by each row of every table that is assigned to ENROLMENT. If the current value of ENROLMENT fails to satisfy this constraint, then the ALTER TABLE statement fails.
  4. PRIMARY KEY ( StudentId, CourseId ) used for constraint. Again, the ALTER TABLE statement fails if the constraint is not satisfied by the current value of ENROLMENT.

Related Discussions:- Adding table constraints

Expressions - syntax, Expressions   An expression is a randomly comple...

Expressions   An expression is a randomly complex combination of the constants, variables, literals, operators, & function calls. The simplest expression is the single variabl

Theory of special creation - origin of life, THEO R Y OF SPECIAL CREATION...

THEO R Y OF SPECIAL CREATION - Life originated on the earth due to natural events by the super natural power. The biblical story of creation of world within six days was p

Example of null operator - nino rule, Example of Null operator - NiNo Rule ...

Example of Null operator - NiNo Rule If we wanted to make HIGHER_OF adhere to "NULL in, NULL out"-let's call it the NiNo rule-we would have to write something like what is sho

Anatomy of a command, Anatomy of a Command Figure, showing a simple S...

Anatomy of a Command Figure, showing a simple SQL command, is almost identical to its counterpart in the theory book. The only difference arises from the fact that SQL uses a

Sql queries-oracle , 1- You can check attribute names from each table in D...

1- You can check attribute names from each table in DBF11 by running for example:  desc dbf11.Member;  desc dbf11.Agent;  desc dbf11.Producer; Because some attribute names in

Overloading, Overloading The PL/SQL overloads the subprogram names. T...

Overloading The PL/SQL overloads the subprogram names. That is, you can use similar name for few different subprograms as long as their formal parameters differ in the number

Fetching from a cursor variable, Fetching from a Cursor Variable The F...

Fetching from a Cursor Variable The FETCH statement retrieve rows one at a time from the product set of a multi-row query. The syntax for the same is as shown: FETCH {curso

Effects of null for union - sql, Effects of NULL for union - SQL The ...

Effects of NULL for union - SQL The treatment of NULL in invocations of EXCEPT is as for UNION. This is different from its treatment in those of NOT IN and quantified compari

Records - syntax, Records Records are the items of the type RECORD. The...

Records Records are the items of the type RECORD. The Records have exclusively named fields that can store the data values of various types. And hence, a record treat associate

Loop labels- iterative control, Loop Labels Like the PL/SQL blocks, loop...

Loop Labels Like the PL/SQL blocks, loops can also be labeled. The label, an undeclared identifier enclosed by double angle brackets, should appear at the beginning of the LOOP

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