Natural join - sql, PL-SQL Programming

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.
Posted Date: 1/18/2013 4:46:02 AM | Location : United States







Related Discussions:- Natural join - sql, Assignment Help, Ask Question on Natural join - sql, Get Answer, Expert's Help, Natural join - sql Discussions

Write discussion on Natural join - sql
Your posts are moderated
Related Questions
Keyword and Parameter Description select_statement: This is a query which returns a result set of the rows. Its syntax is such that of select_ into_statement without the IN

Example of EXCEPT Operator - SQL Example, like its counterpart in the theory book, illustrates the convenience of allowing any table expression to be the source for an INSERT

How Calls Are Resolved? The figure shows that how the PL/SQL compiler resolves the subprogram calls. When the compiler encounters the procedure or function call, it tries to di

Change Sql file into CSV for product registration on Magento Project Description: I have a set of files that are in Sql format and could like for a developer to help me with

BEGIN Parameter Description in pl sql: BEGIN: This keyword signals the beginning of the executable section of a PL/SQL block, that contains executable statements. The execut

Need for Dynamic SQL: You need dynamic SQL in the situations as follows: 1) You would like to execute a SQL data definition statement (like CREATE), a data control statemen

Application to Export Excel Data to MSSQL Server table I am having a table available in excel format and features the subsequent: - Some text is in Arabic (e.g. UTF-8 encodin

Recursive Subprograms The recursive subprogram is the one that calls itself. Think of a recursive call as a call to a few other subprograms that does the similar task as your

DECLARE : This keyword signals the beginning of the declarative section of the PL/SQL block, that contains local declarations. The Items declared locally exist only within the

Defining Autonomous Transactions To define an autonomous transaction, you use the pragma (compiler directive) AUTONOMOUS_TRANSACTION. The pragma instructs the PL/SQL compiler