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

Raise_application_error, Raise_application_error -  procedure of package D...

Raise_application_error -  procedure of package DBMS_STANDARD , allows to issue an user_defined error messages by stored sub-program or database trigger.

Pl/sql engine, Architecture The PL/SQL run-time system and compilation ...

Architecture The PL/SQL run-time system and compilation is a technology, not an independent product. Consider this technology as an engine that compiles and executes the PL/SQL

What is a collection, What Is a Collection The collection is an ordered...

What Is a Collection The collection is an ordered group of elements, all of similar type (for e.g. the grades for a class of students). Each element has a unique subscript whic

Second step at defining type sid in sql, Second Step at defining type SID i...

Second Step at defining type SID in SQL CREATE TYPE SID AS VARCHAR(5) ; Explanation: TYPE SID announces that a type named SID is being defined to the system.

Mutual recursion, Mutual Recursion The Subprograms are mutually recursi...

Mutual Recursion The Subprograms are mutually recursive if they directly or indirectly call each other. In the illustration below, the Boolean functions odd & even, that dete

Character types in pl/sql, Character Types The Character types allow yo...

Character Types The Character types allow you to store alphanumeric data, represent words and text, and manipulate the character strings. CHAR You use the CHAR dataty

Predicate - sql, Predicate - SQL Consider the declarative sentence-a p...

Predicate - SQL Consider the declarative sentence-a proposition-that is used to introduce this topic:  "Student S1, named Anne, is enrolled on course C1." Recall that th

Pascal programming and mysql programming, I have a Pascal Source file that ...

I have a Pascal Source file that needs to be compiled into a Service. In addition, there are various functions (Pascal Procedures I guess) that need to be created to Read and Write

Primary key - sql, Primary Key - SQL A PRIMARY KEY specification carri...

Primary Key - SQL A PRIMARY KEY specification carries an implicit NOT NULL constraint on each column of the specified key. When more than one key constraint is required, the k

Understanding varrays, Understanding Varrays The Items of type VARRAY ar...

Understanding Varrays The Items of type VARRAY are termed as the varrays. They permit you to relate a single identifier with the whole collection. This relationship lets you man

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