Indeterminacy in sql, PL-SQL Programming

Assignment Help:

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?


Related Discussions:- Indeterminacy in sql

Exceptions are raised - Using Raise statement, How Exceptions Are Raised ...

How Exceptions Are Raised By the run-time system, the internal exceptions are raised implicitly as are user-defined exceptions that you have related with an Oracle error number

Renaming columns - sql, Renaming Columns - SQL SQL has no direct count...

Renaming Columns - SQL SQL has no direct counterpart of RENAME. To derive the table on the right in Figure 4.4 from the table on the left, Tutorial D has IS_CALLED RENAME ( St

Declare keyword description in pl sql, DECLARE : This keyword signals t...

DECLARE : This keyword signals the beginning of the declarative section of the PL/SQL block, that contains local declarations. The Items declared locally exist only within the

Functions in pl/sql, Functions   The function is a subprogram that cal...

Functions   The function is a subprogram that calculates a value. The Functions and procedures are structured similar, except that the functions have a RETURN clause. You can

Use tsql function sql server 2012, I want someone to write a TSQL function ...

I want someone to write a TSQL function that returns the name of the ODBC DSN. I will use the queries below, to get information about the connection, but none of these return th

Joining in sql, Joining in SQL Joining IS_CALLED and IS_ENROLLED_ON in...

Joining in SQL Joining IS_CALLED and IS_ENROLLED_ON in SQL SELECT * FROM IS_CALLED NATURAL JOIN IS_ENROLLED_ON This is an example of an SQL table expression. I have been

Using bulk collect clause- bulk bind performance improvement, Using the BUL...

Using the BULK COLLECT Clause The keywords BULK COLLECT specify the SQL engine to bulk-bind output collections before returning them to the PL/SQL engine. You can use these ke

Sqls counterpart of the key words, SQLs counterpart of the key words: ...

SQLs counterpart of the key words: The text from the opening parenthesis to the end of the fourth line specifies the declared type of the table, meaning that every table ever

Calculate the total shopper spending, Many of the reports generated from th...

Many of the reports generated from the system calculate the total dollars in purchases for a shopper. Complete the following steps to create a function named TOT_PURCH_SF that acce

Definition of from - sql, Definition of FROM - SQL Recall that the ope...

Definition of FROM - SQL Recall that the operand of FROM is denoted by a commalist, each element of that commalist being a table expression optionally accompanied by a range v

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