Use of table comparisons - sql, PL-SQL Programming

Use of Table Comparisons - SQL

Table comparisons where it is noted that although table expressions cannot be compared, we have TABLE (t) to convert a table expression t into a value expression of type ROW ( r ) MULTISET, where r is the row type of t. However, the only operator in SQL for comparing two multisets is "=", so SQL has no direct counterparts of examples, which use "⊆", and nor does this chapter.

Those examples are shown merely to demonstrate that every constraint that can be expressed as an invocation of IS_EMPTY can be formulated alternatively as an invocation of "⊆". If SQL were to have a counterpart of that operator, it would presumably have to be an "is submultiset of " operator, where m1 is a submultiset of m2 if and only if each element of m1 appears at least as many times in m2 as it does in m1. But SQL doesn't have such an operator.

Posted Date: 1/18/2013 7:45:28 AM | Location : United States







Related Discussions:- Use of table comparisons - sql, Assignment Help, Ask Question on Use of table comparisons - sql, Get Answer, Expert's Help, Use of table comparisons - sql Discussions

Write discussion on Use of table comparisons - sql
Your posts are moderated
Related Questions
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

"Not Enforced" Table Constraints A constraint that is not enforced is not really a constraint within the meaning of the act, but SQL does have such a concept and it needs to b

Fetching with a Cursor The FETCH statements retrieve the rows in the result set one at a time. After each and every fetch, the cursor advance to the next row in the result set

Using LOCK TABLE You use the LOCK TABLE statement to lock the whole database tables in the specified lock mode so that you can share or deny the access to them. For illustrati

Semidifference via EXCEPT and JOIN - SQL SELECT * FROM (SELECT StudentId FROM IS_CALLED WHERE Name = 'Devinder' EXCEPT DISTINCT CORRESPONDING SELECT StudentId

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

Why Use Cursor Variables ? Primarily, you use the cursor variables to pass the query result sets between the PL/SQL stored subprograms and different clients. Neither PL/SQL nor

Literature review

Parameter Default Values As the illustration below shows, you can initialize the IN parameters to the default values. In that way, you can pass various numbers of actual par

Effects of NULL The numeric variable X, perhaps of type INTEGER, might be assigned NULL. In that case the result of evaluating X + 1 is NULL, and so SET Y = X + 1 assigns NULL