Semijoin and composition - sql, PL-SQL Programming

Assignment Help:

Semijoin and Composition - SQL

For semijoin, the dyadic relational operator MATCHING, defined thus:

r1 MATCHING r2, where r1 and r2 are relations such that r1 JOIN r2 is defined, is equivalent to

(r1 JOIN r2) {r1-attrs}

where r1-attrs is a commalist containing all and only the attribute names of r1.

and the example

COURSE MATCHING EXAM_MARK

is given as a relational expression for the predicate, "There exist a student StudentId and a mark Mark such that StudentId sat the exam and scored Mark marks for course CourseId and CourseId is entitled Title" (which could be abbreviated to "At least one student sat the exam for Course CourseId, entitled Title"). The resulting relation consists of just those tuples in COURSE that have at least one matching tuple in EXAM_MARK.


Related Discussions:- Semijoin and composition - sql

Definition of cross join - sql, Definition of CROSS JOIN - SQL Let s ...

Definition of CROSS JOIN - SQL Let s = t1 CROSS JOIN t2, where t1 and t2 are table expressions optionally accompanied by range variables. Then: Note: Here T denotes Table

Controlling cursor variables, Controlling Cursor Variables You use 3 s...

Controlling Cursor Variables You use 3 statements to control the cursor variable: OPEN-FOR, FETCH, & CLOSE. At First, you OPEN a cursor variable FOR a multi-row query. Then, y

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

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

Using rollback - , Using ROLLBACK The ROLLBACK statements end the pres...

Using ROLLBACK The ROLLBACK statements end the present transaction and undo any change made during the transaction. The Rolling back is helpful for two reasons. Firstly, if yo

Dynamic ranges- iterative control, Dynamic Ranges The PL/SQL lets you det...

Dynamic Ranges The PL/SQL lets you determine the loop range dynamically at run time, as the example below shows: SELECT COUNT(empno) INTO emp_count FROM emp; FOR i IN 1..emp_cou

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

Oracle 9i features, Bitmap Join Indexes - This feature will increase th...

Bitmap Join Indexes - This feature will increase the performance and detains the size and format of your databases in data Character Semantics and Globalization -This featur

Transaction control, Transaction Control The Oracle is transaction orie...

Transaction Control The Oracle is transaction oriented; that is, Oracle uses the transactions to make sure the data integrity. The transaction is a sequence of SQL data manip

%isopen - explicit cursor attributes, %ISOPEN The %ISOPEN yields TRUE ...

%ISOPEN The %ISOPEN yields TRUE if its cursor or cursor variable is open; or else, the %ISOPEN yields FALSE. In the illustration, you use the %ISOPEN to select an action:

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