Enrolment was split - sql, PL-SQL Programming

Assignment Help:

Enrolment was split - SQL

Example shows how relvars IS_CALLED and IS_ENROLLED_ON can be derived from the original ENROLMENT relvar, using projection in the initial assignment to those relvars. Here is how the same effect can be achieved in SQL:

Example: Splitting ENROLMENT

CREATE TABLE IS_CALLED

AS (SELECT DISTINCT StudentId, Name FROM ENROLMENT)

WITH DATA;

ALTER TABLE IS_CALLED ADD CONSTRAINT PRIMARY KEY ( StudentId );

CREATE TABLE IS_ENROLLED_ON

AS (SELECT DISTINCT StudentId, CourseId FROM ENROLMENT)

WITH DATA;

ALTER TABLE ADD CONSTRAINT PRIMARY KEY ( StudentId, CourseId ) ;

DROP TABLE ENROLMENT;

Explanation:

  • CREATE TABLE IS_CALLED announces that what follows defines a base table named IS_CALLED.
  • AS (SELECT DISTINCT StudentId, Name FROM ENROLMENT) specifies that the columns of ENROLMENT and their declared types are as in the specified expression.
  • WITH DATA additionally specifies that the table resulting from the specified expression is to be the initial value of IS_CALLED.
  • ALTER TABLE IS_CALLED ADD PRIMARY KEY ( StudentId ) specifies a constraint to the effect that no two distinct rows having the same StudentId value can ever appear simultaneously in IS_CALLED. Note that this constraint has to be given as a separate statement from the one that creates the base table. If the key word DISTINCT had been omitted, the CREATE TABLE statement would have succeeded but the ALTER TABLE statement would have failed because the required constraint would have been violated by the two appearances of the row for student S1, Anne.
  • Similar comments apply to the CREATE and ALTER TABLE statements for IS_ENROLLED_ ON, but in the equivalent example noted that the specification KEY {StudentId, CourseId}, required by Tutorial D, is theoretically redundant because the entire heading is always a superkey. Here, the corresponding ALTER TABLE statement is not redundant because in the absence of any key constraints SQL allows the same row to appear several times simultaneously in the same base table.
  • DROP TABLE ENROLMENT destroys the variable we have no further use for.

Related Discussions:- Enrolment was split - sql

Sql outer join, SQL outer join SELECT * FROM IS_CALLED NATURAL LEFT...

SQL outer join SELECT * FROM IS_CALLED NATURAL LEFT JOIN IS_ENROLLED_ON Note that adding LEFT to an invocation of CROSS JOIN has no effect unless the right-hand operand

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

Cursors, What is Cursors how to use it in Real time application ?

What is Cursors how to use it in Real time application ?

Relational algebra - sql, Relational Algebra - SQL It describes some ...

Relational Algebra - SQL It describes some operators, that together constitute an algebra that is not only relationally complete but also irreducibly so (very nearly- apart f

Implicit cursor attributes, Implicit Cursor Attributes The Implicit cur...

Implicit Cursor Attributes The Implicit cursor attributes returns the information about the execution of an INSERT, DELETE, UPDATE, or SELECT INTO statement. The cursor attribu

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

Bulk fetching - bulk bind performance improvement, Bulk Fetching The i...

Bulk Fetching The illustration below shows that you can bulk-fetch from a cursor into one or more collections: DECLARE TYPE NameTab IS TABLE OF emp.ename%TYPE; TYPE S

Components of an object type - parameter self, Parameter SELF in pl/sql ...

Parameter SELF in pl/sql The MEMBER methods recognize a built-in parameter named SELF that is an instance of the object type. Whether declared explicitly or implicitly, it is

Write sql queries, Write SQL queries to solve the following specifications....

Write SQL queries to solve the following specifications. Include the query AND THE OUTPUT.  A screen dump of the output is acceptable. Show as many rows as you can. A screen dump i

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

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