Joining in sql, PL-SQL Programming

Assignment Help:

Joining in SQL

Joining IS_CALLED and IS_ENROLLED_ON in SQL

SELECT * FROM IS_CALLED NATURAL JOIN IS_ENROLLED_ON

This is an example of an SQL table expression. I have been assuming you are already familiar with the SELECT-FROM-WHERE structure for certain table expressions. Here an explanation in a different style from that found in the SQL text books, appealing to the concept of operator invocation.

384_Joining in SQL.png

Explanation

  • Example is an invocation of the SQL operator SELECT and for that reason I shall refer to such table expressions as SELECT expressions.
  • Here the SELECT operator operates on the table denoted by the table expression FROM IS_ CALLED NATURAL JOIN IS_ENROLLED_ON, an invocation of the operator FROM. I shall call such table expressions FROM expressions.
  • The FROM operator here is operating on the table denoted by the table expression IS_CALLED NATURAL JOIN IS_ENROLLED_ON, an invocation of the operator NATURAL JOIN.
  •  NATURAL JOIN here is operating on the tables denoted by the table expressions IS_CALLED and IS_ENROLLED_ON, each in turn denoting the table that is the current value of the variable (base table) of that name.
  • NATURAL JOIN is almost equivalent to Tutorial D's JOIN. It differs only in being noncommutative because of the ordering to the columns of an SQL table. The common columns appear first in the result, in the order in which they appear in the left operand. Then come the remaining columns of the left operand, followed by the remaining columns of the right operand. As in Tutorial D, common columns must be of the same type in both operands.
  • FROM is an operator that takes a commalist of one or more table expressions. In this example the list has just one element, IS_CALLED NATURAL JOIN IS_ENROLLED_ON, and the result is that table. An invocation of FROM is usually referred to as a FROM clause. A FROM clause is not permitted to exist in isolation-it must appear in some containing SELECT expression. Similarly, some table expressions are permitted only when they appear as elements of a FROM clause. Simple table names and invocations of NATURAL JOIN are a case in point. The result of a FROM clause must always be operated on by some other clause. In Example it is operated on by a SELECT clause. It can also be operated on by any clause that immediately follows it syntactically, such as a WHERE clause, for example. As we shall see, SQL dictates a strict order in which the clauses of a SELECT expression must appear. Evaluation always starts at the FROM clause, then proceeds forwards from clause to clause, then finally back to the SELECT clause.

Related Discussions:- Joining in sql

Ssrs report writing, SSRS Report Writing Project Description: This re...

SSRS Report Writing Project Description: This report is part of a larger project to make a SQL Server Reporting Service (SSRS) based reporting solution. There can be more rep

Origin of earth - big bang hypothesis, ORIGIN OF EARTH - BIG-BAN G HY...

ORIGIN OF EARTH - BIG-BAN G HYPOTHESIS - Origin of life is linked to origin of earth. Cosmos, the Universe originated 10-20 billion years ago by Big Bang (thermonu

Subprograms, What Are Subprograms? The Subprograms are named PL/SQL blo...

What Are Subprograms? The Subprograms are named PL/SQL blocks which can take parameters and be invoked. The PL/SQL has 2 types of subprograms known as the procedure s and func

Inserting objects in pl sql, Inserting Objects: You can use the INSERT...

Inserting Objects: You can use the INSERT statement to add objects to an object table. In the illustration below, you insert a Person object into the object table persons:

Currval and nextval - sql pseudocolumns, CURRVAL and NEXTVAL The serie...

CURRVAL and NEXTVAL The series is a schema object which generates the sequential numbers. Whenever you form a sequence, you can specify its primary value and an increment. T

Use of count in sql, Use of COUNT in SQL It describes and discusses va...

Use of COUNT in SQL It describes and discusses various general methods of expressing constraints, eventually noting that support for "=" with relation operands is sufficient f

Overloading method in pl/sql, Overloading: Similar to packaged subprog...

Overloading: Similar to packaged subprograms, methods of the same type can be overloaded. That is, you can use similar name for various methods if their formal parameters diff

Package specification in pl/sql , Package Specification The package sp...

Package Specification The package specifications contain the public declarations. The scopes of these declarations are local to your database representation and global to the

Example of null operator - nino rule, Example of Null operator - NiNo Rule ...

Example of Null operator - NiNo Rule If we wanted to make HIGHER_OF adhere to "NULL in, NULL out"-let's call it the NiNo rule-we would have to write something like what is sho

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