Already have an account? Get multiple benefits of using own account!
Login in your account..!
Remember me
Don't have an account? Create your account in less than a minutes,
Forgot password? how can I recover my password now!
Enter right registered email to receive password!
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?
Question 1 . Compare SQL and PL/SQL Question 2 . Write a database trigger to implement the following check condition Given the following table
PL SQL Code Review HEADER ELEMENTS File Name Clear, meaningful and descriptive about main objective of the file. Multiple words are joined using underscores which adh
Question: (a) The objective of query optimization is to choose the most efficient strategy for implementing a given relational query, thereby improving the system performance. On
Updating by replacement Syntax: UPDATE ENROLMENT SET Name = 'Ann' WHERE StudentId = SID ('S1'); Note the use of SET, as already noted in connection with direct a
Using DELETE This process has three forms. The DELETE removes all elements from the collection. DELETE(n) removes the nth element from the nested table. When n is null, then D
Project Description: I am looking to change FullCalendar to add/delete sql server data when events are removed or dropped from Calendar. Events should only be included by dra
What Is a Collection The collection is an ordered group of elements, all of similar type (for e.g. the grades for a class of students). Each element has a unique subscript whic
Assignment Statement: The assignment statement sets the present value of the variable, parameter, field, or element. The statement consists of an assignment target followed by
Example of NOT EXISTS in SQL Example: Use of NOT EXISTS CREATE ASSERTION Must_be_enrolled_to_take_exam_alternative1 CHECK ( NOT EXISTS (SELECT StudentId, CourseId
Example of ADD CONSTRAINT in SQL Example: Alternative formulation for MAX_ENROLMENTS ALTER TABLE IS_ENROLLED_ON ADD CONSTRAINT MAX_ENROLMENTS CHECK ((SELECT COUNT (*)
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!
whatsapp: +91-977-207-8620
Phone: +91-977-207-8620
Email: [email protected]
All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd