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

Keyword and parameter description in pl sql, Keyword and Parameter Descript...

Keyword and Parameter Description: label_name: This is an undeclared identifier which optionally labels the PL/SQL block. When used, label_name should be enclosed by the do

User-defined exceptions, User-Defined Exceptions The PL/SQL defines the...

User-Defined Exceptions The PL/SQL defines the exceptions of your own. Dissimilar to the predefined exceptions, the user-defined exceptions should be declared and should be rai

Manipulating local collections - pl/sql, Manipulating Local Collections ...

Manipulating Local Collections Within PL/SQL, to manipulate the local collection, by using the  TABLE and CAST operators . The operands of CAST are a collection declared locally

Parameter and keyword description - select into statement, Parameter and Ke...

Parameter and Keyword Description: select_item: This select_item is a value returned by the SELECT statement, and then assigned to the equivalent variable or field in the

Extension and and in sql, Extension and AND in SQL The theory book giv...

Extension and AND in SQL The theory book gives the following simple example of relational extension in Tutorial D: EXTEND IS_CALLED ADD ( FirstLetter ( Name ) AS Initial )

Execute immediate statement - syntax, EXECUTE IMMEDIATE Statement   Th...

EXECUTE IMMEDIATE Statement   The EXECUTE IMMEDIATE statement prepare (parses) and instantly executes a dynamic SQL statement or an anonymous PL/SQL block. Syntax:

Exceptions are raised - Using Raise statement, How Exceptions Are Raised ...

How Exceptions Are Raised By the run-time system, the internal exceptions are raised implicitly as are user-defined exceptions that you have related with an Oracle error number

Updating variables, Updating Variables For assignment, SQL uses the ke...

Updating Variables For assignment, SQL uses the key word SET, as in SET X = X + 1 (read as "set X equal to X+1") rather than X: = X + 1 as found in many computer languages.

Using exists - collection methods, Using EXISTS The EXISTS(n) returns ...

Using EXISTS The EXISTS(n) returns TRUE if the nth element in a collection exist. Or else, EXISTS(n) returns FALSE. Primarily, you use EXISTS with DELETE to maintain the spars

Pragma restrict_references in pl sql, Using Pragma RESTRICT_REFERENCES: ...

Using Pragma RESTRICT_REFERENCES: The function called from the SQL statements should obey certain rules meant to control the side effects. To check for violation of the rules,

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