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

Procedure, 1. Create a procedure called TAX_COST_SP to accomplish the tax c...

1. Create a procedure called TAX_COST_SP to accomplish the tax calculation task. Keep in mind that the state and subtotal values are inputs into the procedure and the procedure is

Scope rules - user-defined exceptions, Scope Rules You cannot declare ...

Scope Rules You cannot declare an exception twice in the similar block. Though, you can, declare the similar exception in 2 different blocks. The Exceptions declared in a bloc

Return statement, RETURN Statement The RETURN statement instantly compl...

RETURN Statement The RETURN statement instantly completes the execution of a subprogram and returns control to the caller. The Execution then resumes with the statement below t

"not enforced" table constraints - sql, "Not Enforced" Table Constraints ...

"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 b

Example of table literal - sql, Example of Table Literal - SQL Exampl...

Example of Table Literal - SQL Example: A Table Literal (correct version) VALUES ('S1', 'C1', 'Anne'), ('S1', 'C2', 'Anne'), ('S2', 'C1', 'Boris'), ('S3', 'C3'

Declaring records, Declaring Records Whenever you define a RECORD type...

Declaring Records Whenever you define a RECORD type, you may declare records of that type, as the illustration shows: DECLARE TYPE StockItem IS RECORD ( item_no INTEG

When or then key constraints, WHEN or THEN Key Constraints Suppose a t...

WHEN or THEN Key Constraints Suppose a table has two columns representing a period of time throughout which the information conveyed by the other columns is recorded as having

Pl/sql conditional control: if statements, Pl/sql Conditional Control: IF s...

Pl/sql Conditional Control: IF statements Frequently, it is necessary to take the alternative actions depending on the circumstances. The IF statement execute a series of statem

Declare keyword description in pl sql, DECLARE : This keyword signals t...

DECLARE : This keyword signals the beginning of the declarative section of the PL/SQL block, that contains local declarations. The Items declared locally exist only within the

Deriving predicates from predicates in sql, Deriving Predicates from Predic...

Deriving Predicates from Predicates in SQL The corresponding section in the theory book describes how predicates can be derived from predicates using (a) the logical connectiv

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