Table comparison - sql, PL-SQL Programming

Assignment Help:

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 is also a tuple of r2, otherwise false.

r1 ⊇ r2 is equivalent to r2 ⊆ r1

r1 = r2 is equivalent to r1 ⊆ r2 AND r2 ⊆ r1

The question arises as to whether SQL tables can be similarly compared. SQL does not have direct counterparts of ⊆ and ⊇. It does of course have =, but table expressions cannot be used as comparands. However, as we have seen in Examples et seq., the operator TABLE has been available since SQL: 2003 to derive from a given table expression a value of a multiset type whose element type is a row type. In other words, (SELECT * FROM t1) = (SELECT * FROM t2) is illegal but we can obtain the required effect by writing TABLE (SELECT * FROM t1) = TABLE (SELECT * FROM t2). So, to compare two tables, we have to use an operator named TABLE to "convert" them from tables into multisets of rows!

To test for every row of t1 being also a row of t2 we could write, for example, NOT EXISTS (SELECT * FROM t1 EXCEPT SELECT * FROM t2). In fact, SQL's NOT EXISTS is an exact counterpart of Tutorial D's IS_EMPTY operator. However, note carefully that the case where every row in t1 appears in t2 and every row of t2 appears in t1 does not guarantee that t1 and t2 are the same table. Row r might appear twice in t1 but only once in t2, for example.


Related Discussions:- Table comparison - sql

Solve the business problems using sql, Use the MASCOT tables CREDITRS, PORD...

Use the MASCOT tables CREDITRS, PORDS and PAYMENTS to write SQL queries to solve the following business problems. These tables / data are available to you via the USQ Oracle server

Expression in assignment statement - pl sql, Expression: This is a ran...

Expression: This is a randomly complex combination of constants, variables, literals, operators, & function calls. The simplest expression consists of a single variable. If th

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

Example of foreign key constraint - sql, Example of Foreign Key Constraint ...

Example of Foreign Key Constraint Example: Alternative formulation for 6.3 as a foreign key constraint ALTER TABLE EXAM_MARK ADD CONSTRAINT Must_be_enrolled_to_take_exam

Collection methods in pl sql, Collection Methods:   The collection me...

Collection Methods:   The collection method is a built-in function or procedure which operates on the collections and is called using the dot notation. The methods like the C

Using subqueries, Using Subqueries A subquery is a query (typically ...

Using Subqueries A subquery is a query (typically enclosed by parentheses) that appears within another SQL data manipulation statement. If evaluated, the subquery gives a va

Heap sort algorithm in pl sql, I want to implement heap sort algorithm in p...

I want to implement heap sort algorithm in pl sql please share the source code for guidance

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

Exception handling, set serveroutput on declare a number(5); b n...

set serveroutput on declare a number(5); b number(5); c number(5); begin a:=&a; b:=&b; c:=a/b; dbms_output.put_line(c); exception when zero_d

Interesting properties of cross join - sql, Interesting properties of CROSS...

Interesting properties of CROSS JOIN - SQL Compare these with the "interesting properties of JOIN", CROSS JOIN is associative but not commutative. Unlike JOIN and NATURAL JOI

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