Substitution and instantiation - sql, PL-SQL Programming

Substitution and Instantiation - SQL

It shows how NULL might appear in substitution for a parameter of a predicate and how it might thus participate in instantiation of that predicate to yield a proposition. Now consider instantiations of the dyadic predicate a < b. As well as instantiations such as 5 < 10 (a true one) and 9 < 6 (a false one), we now have to entertain the possibility of instantiations such as 5 < NULL, NULL < 6, and NULL < NULL.

In SQL these comparisons evaluate to that intrusive truth value, unknown. It goes on to explain that the extension of a predicate consists exactly of those instantiations of it that evaluate to true, from which we can conclude, of every instantiation that does not appear in the extension, that it is false, in which case it must appear instead in the extension of the negation of that predicate. In SQL, then, the instantiation 5 < NULL, for example, cannot be considered to appear in either the extension of a < b or NOT (a < b). Or so it would appear.

Posted Date: 1/18/2013 3:08:44 AM | Location : United States







Related Discussions:- Substitution and instantiation - sql, Assignment Help, Ask Question on Substitution and instantiation - sql, Get Answer, Expert's Help, Substitution and instantiation - sql Discussions

Write discussion on Substitution and instantiation - sql
Your posts are moderated
Related Questions
Declaring Cursor Variables Once a REF CURSOR type is define by you, and then you can declare the cursor variables of that type in any PL/SQL block or subprogram. In the exampl

Challenge 1 You are required to do the project and write a test plan for it. Demo 4 is a check writer program for employees. In it, the user enters all information about the

Project Description: I want to rebuild it and add better content to it It will include up to 5 forms The data will be saved on SQL server and the data access layer could b

Project Description: I want a small relational database to be built. I want the database to have the subsequent information tables: Employee Information Document storage

Using COMMIT The COMMIT statements end the present transaction and make permanent any changes made during that transaction. Till you commit the changes, other users cannot acc

In Packages The Forward declarations also group logically related subprograms in the package. The subprogram specifications go in the package specification, & the subprogram b

Datatype Conversion At times it is necessary to convert a value from one datatype to another. For e.g. if you want to inspect a rowid, you should convert it to a character stri

Remote Operations: As the illustration shows below, the PL/SQL subprograms can execute the dynamic SQL statements which refer to the objects on a remote database: PROCEDURE

Question: Consider the following relations (primary keys are underlined): AUTHOR (ANo, aname, address, speciality) PUBLISHER (PNo, pname, Location) BOOK (BNo, Title, ISBN,

%TYPE: This attribute gives the datatype of a formerly declared collection, cursor variable, object, field, record, database column, or variable. Datatype: This is simply