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!
Projection in SQL - correct version
Student StudentId is enrolled on some course.
SELECT DISTINCT StudentId FROM IS_ENROLLED_ON
In more complicated examples it is sometimes quite difficult to tell whether omission of DISTINCT would give rise to duplicate rows. It might therefore seem good advice to always write DISTINCT. Indeed, I would certainly advocate such practice to students having to write SQL expressions in solutions to questions in exam papers, for example, but if it were followed blindly in commercial systems, then many queries would run very much slower than need be because typical SQL implementations have little or nothing in the way of built-in intelligence to recognize cases where duplicate rows cannot possibly arise. Although such intelligence is quite feasible within acceptable limits (and was used in Business System 12, for example), the inclusion of DISTINCT allows SQL implementations to place the responsibility for duplicate elimination on the user.
Ending Transactions A good quality programming practice is to commit or roll back every transaction explicitly. Whether you rollback or issue the commit in your PL/SQL program
Data Types in SQL - Interval, Boolean INTERVAL for values denoting, not intervals (!) but durations in time, such as 5 years, 3 days, 2 minutes, and so on. BOOLEAN, con
Built-In Functions The PL/SQL provides a lot of powerful functions to help you to manipulate the data. These built-in functions fall into the categories as shown below: error r
EXIT-WHEN The EXIT-WHEN statement permits a loop to complete conditionally. Whenever the EXIT statement is encountered, the condition in the WHEN clause is computed. When the co
%NOTFOUND The %NOTFOUND is logical, opposite of the %FOUND. The %NOTFOUND yields FALSE if the last fetch returned a row, or TRUE when the final fetch failed to return a row. I
Example of COALESCE operator Example: Give the total of marks for each exam (simplified solution) SELECT CourseId, COALESCE ((SELECT SUM (Mark) FROM EXAM_MARK AS EM
Using COUNT The COUNT returns the number of elements that a collection presently contains. For instance, when a varray projects contains 15 elements, then the following IF con
Type versus Representation Confusion in SQL This describes how a value might have two or more distinct representations. For example, user-defined type POINT might have a decla
Project Description: We organize an online system called ACPAS we have created a project called EVO that can be use by our customers to integrate their web sites with the Acpas
Perform the following queries on the Hospital1.DB using SQL Anywhere (START EARLY!). a. Which patients have purchased the drug "Tylenol"? List the names and addresses. Arrange the
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