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

Exit statement - syntax, EXIT Statement   You can use the EXIT stateme...

EXIT Statement   You can use the EXIT statement to exit a loop. The EXIT statement has 2 forms: the conditional EXIT WHEN and the unconditional EXIT. With the either form, you

Effects of null in table literal, Effects of NULL in Table Literal Whe...

Effects of NULL in Table Literal When a VALUES expression appears as the source value for an SQL INSERT statement, the key word NULL can appear as a field value, such that for

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

Assignment source not a literal - variable, Assignment Source Not a Literal...

Assignment Source Not a Literal - Variable Syntax: SET SN = SID (SUBSTRING (SN.C FROM 1 FOR 1)||'5');

Declarations in sql-pl/sql, Declarations in SQL Your program stores value...

Declarations in SQL Your program stores values in the variables and constants. As the program executes, the value of the variables can change, but the values constants cannot.

%isopen - explicit cursor attributes, %ISOPEN The %ISOPEN yields TRUE ...

%ISOPEN The %ISOPEN yields TRUE if its cursor or cursor variable is open; or else, the %ISOPEN yields FALSE. In the illustration, you use the %ISOPEN to select an action:

Between and not between operator in sql, BETWEEN and NOT BETWEEN Operator i...

BETWEEN and NOT BETWEEN Operator in SQL Example: Restricting exam marks to between 0 and 100 CREATE ASSERTION Marks_between_0_and_100 CHECK (NOT EXISTS (SELECT * FROM

What are decision support systems, (a) What are decision support systems, a...

(a) What are decision support systems, and what role do they play in the business environment? (b) Data warehousing is defined as "a subject-oriented, integrated, non-volatile c

Character types, ROWID and UROWID Internally, every database table has ...

ROWID and UROWID Internally, every database table has a ROWID pseudo column that stores binary values known as rowids. Each rowid shows the storage address of a row. A physical

Best practices/Data Warhousing, What are 3 good practices of modeling and/o...

What are 3 good practices of modeling and/or implementing data warehouses?

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