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

Change sql file into csv for product registration, Change Sql file into CSV...

Change Sql file into CSV for product registration on Magento Project Description: I have a set of files that are in Sql format and could like for a developer to help me with

Laws / rules associated with evolution, LAWS / RULES - Dollo's Law    ...

LAWS / RULES - Dollo's Law                     :           Living organisms do exhibit evolutionary irreversibility or evolution is irreversible. Williston's Law

Dbms, DBMS: The answer to this question is of course given in of the t...

DBMS: The answer to this question is of course given in of the theory book. This book is concerned with SQL DBMSs and SQL databases in particular. Soon we will be looking a

Package utl file in pl/sql, UTL_FILE: The Package UTL_FILE permits you...

UTL_FILE: The Package UTL_FILE permits your PL/SQL programs to read & write operating system (OS) text files. It gives a restricted version of the standard OS stream file I/O,

Data types, Datatypes Every constant and variable has a datatype that s...

Datatypes Every constant and variable has a datatype that specifies the storage format, constraints, and the valid range of values. The PL/SQL gives a variety of predefined dat

Use external routines - improve performance of application, Use External Ro...

Use External Routines The PL/SQL is particular for the SQL transaction processing. Therefore, several tasks are more quickly completed in a lower-level language like C that is

Package standard in pl/sql, Package STANDARD package named STANDARD d...

Package STANDARD package named STANDARD defines the PL/SQL atmosphere. The package specification globally declares the exceptions, types, and subprograms that are available a

Logical connectives - sql, Logical Connectives - SQL SQL's extended t...

Logical Connectives - SQL SQL's extended truth tables in which the symbol, for unknown, appears along with the usual T and F. Negation (NOT, ¬) Conjunction (

I want online credit application website, Project Description: We organi...

Project Description: We organize an online system called ACPAS we have created a project called EVO that can be use by our customers to integrate their web sites with the Acpas

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