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

Variables and constants in pl/sql, V ariables and Constants in PL/SQL ...

V ariables and Constants in PL/SQL The PL/SQL permits you to declare constants and variables, and then use them in SQL and procedural statements anywhere in the expression. Th

Running the pl/sql wrapper, Running the PL/SQL Wrapper To run the PL/SQ...

Running the PL/SQL Wrapper To run the PL/SQL Wrapper, go through the wrap command at your operating system prompt by using the syntax as shown: wrap iname=input_file [oname=

Data type conversion, Datatype Conversion At times it is necessary to c...

Datatype Conversion At times it is necessary to convert a value from one datatype to another. For e.g. if you want to inspect a rowid, you should convert it to a character stri

Write a program, to write a heap sort program usin pl-sql

to write a heap sort program usin pl-sql

Example of coalesce operator - sql, Example of COALESCE operator Examp...

Example of COALESCE operator Example: Give the total of marks for each exam (simplified solution) SELECT CourseId, COALESCE ((SELECT SUM (Mark) FROM EXAM_MARK AS EM

PROCEDURE, Create a procedure named DDPROJ_SP that retrieves project inform...

Create a procedure named DDPROJ_SP that retrieves project information for a specific project based on a project ID. The procedure should have two parameters: one to accept a projec

Bulk fetching - bulk bind performance improvement, Bulk Fetching The i...

Bulk Fetching The illustration below shows that you can bulk-fetch from a cursor into one or more collections: DECLARE TYPE NameTab IS TABLE OF emp.ename%TYPE; TYPE S

Boolean values-assignments in pl/sql, Boolean Values Only the values TRU...

Boolean Values Only the values TRUE, FALSE, & NULL can be assigned to a Boolean variable. For illustration, given the declaration DECLARE done BOOLEAN; the following statements

Query, ALTER TABLE bb_basketitem ADD CONSTRAINT bitems_qty_ck CHECK (quan...

ALTER TABLE bb_basketitem ADD CONSTRAINT bitems_qty_ck CHECK (quantity BEGIN INSERT INTO bb_basketitem VALUES (88,8,10.8,21,16,2,3); END; Brewbean’s wants to add a check

Union without corresponding - sql, UNION without CORRESPONDING - SQL T...

UNION without CORRESPONDING - SQL The use of UNION without CORRESPONDING. Example is merely by omitting CORRESPONDING, but only because the operands have identical SELECT clau

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