Natural join - sql, PL-SQL Programming

Assignment Help:

Natural Join - SQL

In the absence of NATURAL JOIN Example has to be replaced by something rather more longwinded, as shown in Example.

Example: Joining IS_CALLED and IS_ENROLLED_ON in original SQL

SELECT IC.StudentId, Name, CourseId

FROM IS_CALLED AS IC, IS_ENROLLED_ON AS IE

WHERE IC.StudentId = IE.StudentId

866_Joining in SQL.png

Explanation

  • The FROM clause now has two elements. When there are two elements, t1 and t2, the result is equivalent to t1 CROSS JOIN t2, which is SQL's counterpart of t1 TIMES t2 in Tutorial D. However, TIMES requires its operands to have disjoint headings, whereas CROSS JOIN is defined for all pairs of SQL tables. When t1 and t2 each have a column named c, the result has two columns named c. In general, when t1 has m columns named c and t2 has n, t1 CROSS JOIN t2 has m+n columns named c.
  • Following the FROM clause is a WHERE clause, denoting an invocation of the operator WHERE. The operands are the table resulting from the FROM clause and the condition following the word WHERE. SQL's WHERE operator is equivalent to Tutorial D's operator of the same name when its table operand represents a relation.
  • The result of the FROM clause has two columns of the same name, StudentId. The condition specified in the WHERE clause uses range variables, IC and IE, to distinguish between these two columns. The distinction is possible here, thanks to the fact that the same column name isn't used more than once in either of the two operand tables (as we shall see later, that is a condition that does not always apply, even though the same column name cannot be used more than once in a base table).
  • The range variables are defined in the FROM clause alongside the table expressions to which they apply. The key word AS separating the table expression from the range variable name is optional. If the table expression consists of just a table name, unaccompanied by a range variable, then that table name serves also as a range variable name.
  • A range variable is so-called because it is considered to "range over" each element in turn of a collection, the collection in the example at hand being the rows of a table. Note carefully that although the expression IE.StudentId is a column reference, it is not a column name. It references a particular column named StudentId. The prefix "IE." is required because without it the column reference would be ambiguous.

Related Discussions:- Natural join - sql

Using exists - collection methods, Using EXISTS The EXISTS(n) returns ...

Using EXISTS The EXISTS(n) returns TRUE if the nth element in a collection exist. Or else, EXISTS(n) returns FALSE. Primarily, you use EXISTS with DELETE to maintain the spars

Do you know anyone that can do this type of coding or not?, Task 2 [12 mark...

Task 2 [12 marks] Write the package body for the following package specification (the detailed description of each function and procedure is provided in the appendix below). Place

Processing transactions, Processing Transactions This part describes ho...

Processing Transactions This part describes how to do the transaction processing. You learn the fundamental techniques that safeguard the consistency of your database, involvin

Keyword and parameter description - goto statement, Keyword and Parameter D...

Keyword and Parameter Description: label_name: This is an undeclared identifier which labels an executable statement or the PL/SQL block. You can use a GOTO statement to

Autonomous versus nested transactions, Autonomous versus Nested Transaction...

Autonomous versus Nested Transactions Though an autonomous transaction is started by the other transaction, it is not a nested transaction for the reasons shown below: (i)

Benefit of the dynamic sql pl sql, Benefit of the dynamic SQL: This pa...

Benefit of the dynamic SQL: This part shows you how to take full benefit of the dynamic SQL and how to keep away from some of the common pitfalls. Passing the Names of Sc

Theory of catastrophism or catalysm - origin of life, THEO R Y OF CATASTR...

THEO R Y OF CATASTROPHISM OR CATALYSM (CUVIER 1769-1832) - The world has passed thorugh several stages and at the end of each stage there was a catastrophe killing all the

Sql query for testing triggers and stored procedures , Description: Dem...

Description: Demonstrate your knowledge of PL/SQL programming by writing and thoroughly testing triggers and stored procedures associated with an e-commerce application that pr

Join and and in sql, JOIN and AND in SQL In this Section is all about ...

JOIN and AND in SQL In this Section is all about one operator, JOIN. SQL's closest counterpart, NATURAL JOIN, has already been covered. Here we look at several other "join" op

Need fullcalendar modifications, Project Description: I am looking to ch...

Project Description: I am looking to change FullCalendar to add/delete sql server data when events are removed or dropped from Calendar. Events should only be included by dra

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