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

Set operators - sql operators, Set Operators The Set operators combine...

Set Operators The Set operators combine the results of the two queries into one result. The INTERSECT returns all the distinct rows selected by both queries. The MINUS returns

Union without corresponding - sql, UNION without CORRESPONDING - SQL T...

UNION without CORRESPONDING - SQL The use of UNION without CORRESPONDING. Example is merely by omitting CORRESPONDING, but only because the operands have identical SELECT clau

Advantages of subprograms, Advantages of Subprograms The Subprograms g...

Advantages of Subprograms The Subprograms give extensibility; that is, tailor the PL/SQL language to suit your requirements. For illustration, if you require a procedure which

Providing results of queries, Providing Results of Queries Expressing ...

Providing Results of Queries Expressing queries in SQL is the (big) subject. Here I present just a simple example to give you the flavour of things to come in those chapters.

Redeclaring predefined exceptions - user-defined exceptions, Redeclaring Pr...

Redeclaring Predefined Exceptions Keep in mind that, the PL/SQL declares predefined exceptions globally in the package STANDARD; Therefore you need not declare them yourself.

Need for dynamic sql - pl sql , Need for Dynamic SQL: You need dynamic...

Need for Dynamic SQL: You need dynamic SQL in the situations as follows: 1) You would like to execute a SQL data definition statement (like CREATE), a data control statemen

Usefulness of data type, Usefulness of Data Type In SQL, as in most c...

Usefulness of Data Type In SQL, as in most computer languages, a type can be used for constraining the values that are permitted to be used for some purpose. In particular, i

Effects of null for table expression, Effects of NULL for Table Expression ...

Effects of NULL for Table Expression Here's an important distinction between expressions denoting tables and expressions denoting multisets of rows: a table expression cannot

Defining autonomous transactions, Defining Autonomous Transactions To ...

Defining Autonomous Transactions To define an autonomous transaction, you use the pragma (compiler directive) AUTONOMOUS_TRANSACTION. The pragma instructs the PL/SQL compiler

What are decision support systems, (a) What are decision support systems, a...

(a) What are decision support systems, and what role do they play in the business environment? (b) Data warehousing is defined as "a subject-oriented, integrated, non-volatile c

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