Closest approximation to relational union - sql, PL-SQL Programming

Assignment Help:

Closest Approximation to Relational Union - SQL

Actually, just as SQL has several varieties of JOIN, it also has several varieties of UNION, none of which is equivalent to the relational operator of that name. The closest approximation to relational union is illustrated in Example.

Example: SQL's closest approximation to relational union

SELECT StudentId

FROM IS_CALLED

WHERE Name = 'Devinder'

UNION DISTINCT CORRESPONDING

SELECT StudentId

FROM IS_ENROLLED_ON

WHERE CourseId = 'C1'

The key word DISTINCT is optional and implied by default (somewhat curiously so, considering that its opposite, ALL, is the default option in the SELECT clause). It specifies that no row is to appear more than once in the result. Thus, there is never a need to include DISTINCT in either of the SELECT clauses, and this would be the case even if the WHERE clause were omitted from the specification of the second operand in Example, allowing the same StudentId value to appear more than once in that operand.

The key word CORRESPONDING specifies that operand columns are to be paired by name, just as in relational union.


Related Discussions:- Closest approximation to relational union - sql

Positional notation, Positional Notation The first procedure call uses...

Positional Notation The first procedure call uses the positional notation. The PL/SQL compiler relates the first actual parameter, account, with the first proper parameter, ac

Defining and declaring collections, Defining and Declaring Collections T...

Defining and Declaring Collections To create the collections, you must define a collection type, and then declare the collections of that type. You can define the VARRAY types a

Package - pl/sql programming, What Is a Package? The package is a sch...

What Is a Package? The package is a schema object that group logically related PL/SQL items, types, and subprograms. The Packages usually have 2 parts, a specification & a bo

Program, heap sort program in pl/sql

heap sort program in pl/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

Updating tables in sql, Updating Tables in SQL The topic of updating b...

Updating Tables in SQL The topic of updating by describing the assignment operator, ":=" in Tutorial D. SQL uses a different syntax for assignment, using the key word SET and

Cursor variables, What Are Cursor Variables  ? The Cursor variables ar...

What Are Cursor Variables  ? The Cursor variables are like C or Pascal pointers that hold the memory location (address) of some item rather of the item itself. Therefore, decl

"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

Library system, Hi,am developing a library system and relating all the tabl...

Hi,am developing a library system and relating all the table is somehow complex,could you kindly assist me

Iterative control: loop statement, Iterative Control: LOOP  Statements T...

Iterative Control: LOOP  Statements The LOOP statement executes a series of statements multiple times. There are 3 forms of LOOP statements: LOOP, WHILE-LOOP, & FOR-LOOP. LOOP

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