Indeterminacy in sql, PL-SQL Programming

Indeterminacy in SQL

Some SQL expressions are actually not function invocations at all in the mathematical sense, being indeterminate-invocations operating on identical input do not always yield the same value. The indeterminate expressions are among those that the standard defines as possibly non-deterministic, but- caveat lector-not all expressions defined as possibly non-deterministic are actually indeterminate from a mathematical viewpoint. For example, the key word USER denotes the userid (officially, the authorization identifier) of the session in which an expression containing that key word is evaluated. Such an expression is defined as possibly non-deterministic by virtue of the appearance of USER, even though invocations in different sessions, in which USER stands for different userids, are clearly different invocations.

For a more general example, a user-defined function can be explicitly declared as either DETERMINISTIC or NOT DETERMINISTIC. In the latter case the "function" is flagged such that all invocations of it are treated as possibly non-deterministic. Regardless of the appropriateness of the term non-deterministic, there is a good reason for categorizing references to the current user (or, for another example, the current time) along with genuine cases of indeterminacy. It concerns constraint declarations. We clearly want to outlaw a constraint condition whose result, when evaluated, depends on the properties of the session in which, or on the time at which, the evaluation takes place. Of course we must also outlaw genuinely indeterminate conditions-a database might satisfy such a condition but later fail to satisfy it even though the database has not been updated in the meantime! The question then arises as to how it is possible for indeterminacy to arise: surely a computer program always gives the same result when invoked with the same input?

Posted Date: 1/18/2013 1:53:25 AM | Location : United States







Related Discussions:- Indeterminacy in sql, Assignment Help, Ask Question on Indeterminacy in sql, Get Answer, Expert's Help, Indeterminacy in sql Discussions

Write discussion on Indeterminacy in sql
Your posts are moderated
Related Questions
Multiset types - SQL An SQL multiset is what in mathematics is also known as a bag-something like a set except that the same element can appear more than once. The body of an

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

Creating and Destroying Base Tables: Example shows an SQL command to create the base table counterpart of the ENROLMENT variable Example  Creating a base table. CREATE T

LIKE Operator You use the LIKE operator to compare the character value to a pattern. The Case is significant. LIKE returns the Boolean value TRUE when the character patterns mat

At times, Brewbean's has changed the id number for existing products. In the past, they have had to add a new product row with the new id to the BB_PRODUCT table, modify all the co

DELETE Command - SQL Loosely speaking, DELETE removes some existing rows from its target table. Suppose the university decides that course C3 is to be withdrawn. Example shows

Closing a Cursor Variable The CLOSE statement disables the cursor variable. After that, the related result set is undefined. The syntax for the same is as shown below: CLOS

Difference between 9i & 10G When Oracle releases any new databases then it are having some discrepancy with them. But 10G is having much difference than oracle 9i has. Oracle

Write a pl/sql block that declares and uses cursors with parameters. In a loop, use a cursor to retrieve the department number and the department name from the departments table

1. Create a procedure called TAX_COST_SP to accomplish the tax calculation task. Keep in mind that the state and subtotal values are inputs into the procedure and the procedure is