Special cases of projection, PL-SQL Programming

Special cases of projection

This section describes the identity projection, r {ALL BUT}, and the projection on no attributes, r { }, which yields TABLE_DUM when r is empty, otherwise TABLE_DEE. As we have already seen, the identity projection is represented in SQL by SELECT * FROM t, but SQL does not recognize the existence of column less tables and so SELECT FROM t is not supported.

 

Posted Date: 1/18/2013 5:13:10 AM | Location : United States







Related Discussions:- Special cases of projection, Assignment Help, Ask Question on Special cases of projection, Get Answer, Expert's Help, Special cases of projection Discussions

Write discussion on Special cases of projection
Your posts are moderated
Related Questions
This is a Customer Management project. Customer data is presented in a text file. The program will load this text data into its DB columns. The data mapping is user definable. User

At times, customers make mistakes in submitting their orders and call to cancel the order. Brewbean’s wants to create a trigger that automatically updates the stock level of all pr

Synonyms You can create the synonyms to provide location transparency for the remote schema objects like tables, views, sequences, stand-alone subprograms, and packages. Though,

Primary Key - SQL A PRIMARY KEY specification carries an implicit NOT NULL constraint on each column of the specified key. When more than one key constraint is required, the k

Using a join on 3 tables, select 5 columns and 10 rows from the 3 tables without the use of a Cartesian product Query: SELECT E.LAST_NAME, E.FIRST_NAME, S.BUILDING, S.BRAN

Using EXTEND To enlarge the size of a collection, use EXTEND. This process has 3 forms. The EXTEND appends one null element to a collection. And the EXTEND(n) appends n null e

LAWS / RULES - Dollo's Law                     :           Living organisms do exhibit evolutionary irreversibility or evolution is irreversible. Williston's Law

"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

Biconditional - SQL The biconditional p ↔ q can be expressed in Tutorial D by p = q and the same is true of SQL. The question then arises as to whether, in SQL, p = q is equiv

I need a query for PL/SQL, selecting names with cursor, goes down the list, assigns usernames (initials001) based on initials in the name. If two names have same initials the user