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

Sql query on hospital database, Perform the following queries on the Hospit...

Perform the following queries on the Hospital1.DB using SQL Anywhere (START EARLY!). a. Which patients have purchased the drug "Tylenol"? List the names and addresses. Arrange the

Using invoker rights in pl sql, Using Invoker Rights: By default, the ...

Using Invoker Rights: By default, the stored procedure executes with the privileges of its definer, not its invoker. These procedures are bound to the schema in which they inh

Primary key, PRIMARY KEY: PRIMARY KEY  indicates that the table is sub...

PRIMARY KEY: PRIMARY KEY  indicates that the table is subject to a key constraint, in this case declaring that no two rows in the table assigned to ENROLMENT can ever have the

Dynamic sql - pl sql, Dynamic SQL: The Most PL/SQL programs do a predi...

Dynamic SQL: The Most PL/SQL programs do a predictable, specific job. For illustration, a stored procedure may accept an employee number and salary increase, and then update t

Update stock levels, At times, customers make mistakes in submitting their ...

At times, customers make mistakes in submitting their orders and call to cancel the order. Brewbean's wants to create a trigger that automatically updates the stock level of all pr

Keyword, what is the use of declare keyword

what is the use of declare keyword

program for employees -ado.net framework , Challenge 1 You are require...

Challenge 1 You are required to do the project and write a test plan for it. Demo 4 is a check writer program for employees. In it, the user enters all information about the

Grouping and ungrouping in sql, Grouping and Ungrouping in SQL Example...

Grouping and Ungrouping in SQL Example specifying EXAM_MARK in place of COURSE in the main FROM clause. Example: Obtaining C_ER2 from EXAM_MARK SELECT CourseId, CAST

Using host arrays - bulk bind performance improvement, Using Host Arrays ...

Using Host Arrays The Client-side programs can use anonymous PL/SQL blocks to bulk-bind input and output host arrays. However, this is the well-organized way to pass the colle

Defining ref cursor types, Defining REF CURSOR Types To make cursor va...

Defining REF CURSOR Types To make cursor variables, you take 2 steps. At first, you define a REF CURSOR type, and then declare the cursor variables of that type. You can defin

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