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

While-loop - iterative control, WHILE-LOOP The WHILE-LOOP statement rela...

WHILE-LOOP The WHILE-LOOP statement relates a condition with the series of statements enclosed by the keywords LOOP and END LOOP, as shown: WHILE condition LOOP sequence_of_sta

Cursor variables as parameters, Cursor Variables As Parameters You can...

Cursor Variables As Parameters You can declare the cursor variables as the formal parameters of the functions and procedures. In the illustration below, you define the REF CUR

Using operator ref - manipulating objects pl sql, Using Operator REF: ...

Using Operator REF: You can retrieve refs by using the operator REF that, like VALUE, takes as its argument a correlation variable. In the illustration below, you retrieve one

Procedure, 1. Create a procedure called TAX_COST_SP to accomplish the tax c...

1. Create a procedure called TAX_COST_SP to accomplish the tax calculation task. Keep in mind that the state and subtotal values are inputs into the procedure and the procedure is

Semidifference and not - sql, Semidifference and NOT - SQL In this sec...

Semidifference and NOT - SQL In this section first describe the relational difference operator, named MINUS. Example here shows SQL's closest counterpart of that operator.

Declaring a cursor, Declaring a Cursor The Forward references are not ...

Declaring a Cursor The Forward references are not allowed in the PL/SQL. Therefore, you must declare a cursor before referencing it in other statements. Whenever you declare a

Number types in pl/sql, Number Types The Number types permit you to sto...

Number Types The Number types permit you to store the numeric data (real numbers, integers, and floating-point numbers), show quantities, and do computations. BINARY_INTEG

Declaring objects in pl/sql, Declaring Objects: You can use the object ...

Declaring Objects: You can use the object types wherever built-in types like CHAR or NUMBER can be used. In the block below, you can declare object r of type Rational. Then, yo

Package standard, Package STANDARD The package named STANDARD defines t...

Package STANDARD The package named STANDARD defines the PL/SQL atmosphere. The package specification globally declares the exceptions, types, and subprograms that are available

Write sql code that will create the writes table, Question: Consider th...

Question: Consider the following relations (primary keys are underlined): AUTHOR (ANo, aname, address, speciality) PUBLISHER (PNo, pname, Location) BOOK (BNo, Title, ISBN,

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