Row counterparts of table operators - sql, PL-SQL Programming

Assignment Help:

Row Counterparts of Table Operators

SQL does not have counterparts tuple rename, tuple projection, tuple extension, tuple join and tuple compose. To obtain the same effects as these operators on row r, one has first to derive the table t consisting of just r, then apply the SQL counterpart of the corresponding relational operator on t, putting parentheses around the table expression so that, so long as the context is appropriate, it becomes a row subquery. For example, if r has fields named a, b, and c, we can simulate a tuple renaming of a tuple projection to obtain the row consisting of just a and b, with b renamed to x, by (SELECT a, x FROM VALUES (r) AS t(a, x, c)).

The snag here is that the columns of a VALUES expression have implementation-dependent names, so we cannot rely on the field names of r being propagated to the table. We therefore have to specify the names in parentheses after the range variable name, t. At least that gives us the slight short cut of renaming b as x on the fly, so to speak.


Related Discussions:- Row counterparts of table operators - sql

Data types, Datatypes Every constant and variable has a datatype that s...

Datatypes Every constant and variable has a datatype that specifies the storage format, constraints, and the valid range of values. The PL/SQL gives a variety of predefined dat

Using set transaction, Using SET TRANSACTION You use the SET TRANSACTI...

Using SET TRANSACTION You use the SET TRANSACTION statement to begin the read-only or read-write transaction, start an isolation level, or assign your present transaction to a

I want database development with analysis tools, Project Description: I ...

Project Description: I want a database for large governmental and private data sets on one country that will be easily extended to other countries in the future. Also, the datab

Write an anonymous block that contains a pl/sql procedure, Write an anonymo...

Write an anonymous block that contains a PL/SQL procedure. The procedure takes two input parameter: oldZip and newZip, and it updates the zipcodes table by replacing all oldZip wit

Parameter modes, Parameter Modes   To define the behavior of formal pa...

Parameter Modes   To define the behavior of formal parameters you use the parameter modes. The 3 parameter modes, IN, OUT, & IN OUT, can be used with any subprogram. Though, a

In out mode - parameter modes, IN OUT Mode An IN OUT parameter passes ...

IN OUT Mode An IN OUT parameter passes initial values to the subprogram being called and return efficient values to the caller. Within the subprogram, an IN OUT parameter acts

Procedural constraint enforcement (triggers) , Procedural Constraint Enforc...

Procedural Constraint Enforcement (Triggers) SQL has an alternative method of addressing database integrity, involving event-driven procedural code. The special procedures th

Left and right joins, Left and Right Joins LEFT OUTER JOIN can be used...

Left and Right Joins LEFT OUTER JOIN can be used when you want to retrieve the data from the main table (table1) even if there is no match in other tables (table_2, table_3...

Sql cursor - syntax, SQL Cursor   The Oracle implicitly opens a cursor...

SQL Cursor   The Oracle implicitly opens a cursor to process each SQL statement not related with an explicit cursor. The PL/SQL refers to the most current implicit cursor as t

Example of check constraints - sql, Example of Check Constraints Examp...

Example of Check Constraints Example: Workaround for when subqueries not permitted in CHECK constraints CREATE FUNCTION NO_MORE_THAN_20000_ENROLMENTS ( ) RETURNS BOOLEAN

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