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!
WHEN or THEN Key Constraints
Suppose a table has two columns representing a period of time throughout which the information conveyed by the other columns is recorded as having been the case. A salary history table for employees, with columns From and To for dates defining the applicable time periods, would be a good example.
A constraint is needed to avoid the possibility of an employee being shown as having two different salaries on the same day, which could happen if two rows for the same employee have overlapping periods indicated by their From and To dates. The term "WHEN/THEN constraint" appeals to the notion of "unpacking" the table so that each row is replaced by one or more rows, one for each date contained in its from-to period: when the relation is unpacked, then the given key constraint (e.g., on employee number and date) is to hold.
Example of Null operator - NiNo Rule If we wanted to make HIGHER_OF adhere to "NULL in, NULL out"-let's call it the NiNo rule-we would have to write something like what is sho
Identifiers You use identifiers to name the PL/SQL program items and units that include constants, variables, cursors, exceptions, cursor variables, subprograms, and packages.
Example of WHEN or THEN Constraints A concrete example showing how SQL supports WHEN/THEN constraints CREATE TABLE SAL_HISTORY (EmpNo CHAR (6), Salary INTEGER NOT NULL,
Advantages of Exceptions Using the exceptions for the error handling has many benefits. Without an exception handling, every time you issue a command, you should ensure for th
Create the four tables and populate them with the given data. Answer the following queries in SQL. 1. Get all part-color/part-city combinations. Note: Here and subsequently, the
Substitution and Instantiation - SQL It shows how NULL might appear in substitution for a parameter of a predicate and how it might thus participate in instantiation of that p
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
Explicit Cursors The set of rows returned by the query can include zero, one, or multiple rows, depending on how many rows meet your search criteria. Whenever a query returns
Declaring Objects: You can use the object types wherever built-in types like CHAR or NUMBER can be used. In the block below, you can declare object r of type Rational. Then, yo
Blocks: The fundamental program unit in the PL/SQL is the block. The PL/SQL block is defined by the keywords BEGIN, DECLARE, EXCEPTION, and END. These keywords partition the b
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