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

Identifiers in pl/sql, Identifiers You use identifiers to name the PL/S...

Identifiers You use identifiers to name the PL/SQL program items and units that include constants, variables, cursors, exceptions, cursor variables, subprograms, and packages.

Package specification in pl/sql , Package Specification The package sp...

Package Specification The package specifications contain the public declarations. The scopes of these declarations are local to your database representation and global to the

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...

Need to change mysql query to pdo, Need to change mysql query to PDO Pro...

Need to change mysql query to PDO Project Description: I want someone to convert me 1 .php file that includes some sql/mysql stuff to PDO is a very small file. Skills requ

When or then key constraints, WHEN or THEN Key Constraints Suppose a t...

WHEN or THEN Key Constraints Suppose a table has two columns representing a period of time throughout which the information conveyed by the other columns is recorded as having

Keyword & parameter description - exception_init pragma, Keyword & Paramete...

Keyword & Parameter Description: PRAGMA: These keywords signify that the statement is a pragma (i.e. compiler directive). The Pragmas are processed at the compile time, n

Cosmozoic theory - origin of life, COSMOZOI C THEORY - Richter (1865...

COSMOZOI C THEORY - Richter (1865) proposed the cosmozoic theory that says that life came by spores (cosmozoa) or other particles from other planets on the earth.

Keyword and parameter description - cursors, Keyword and Parameter Descript...

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

Table comparison - sql, Table Comparison - SQL The following definitio...

Table Comparison - SQL The following definitions for relation comparisons: Let r1 and r2 be relations having the same heading. Then: r1 ⊆ r2 is true if every tuple of r1

Declarations in sql-pl/sql, Declarations in SQL Your program stores value...

Declarations in SQL Your program stores values in the variables and constants. As the program executes, the value of the variables can change, but the values constants cannot.

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