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.
SQL Pseudocolumns The PL/SQL recognizes the following SQL pseudocolumns, that returns the specific data items: LEVEL, NEXTVAL, CURRVAL, ROWID, & ROWNUM. The Pseudocolumns are n
Declarations in SQL Your program stores values in the variables and constants. As the program executes, the value of the variables can change, but the values constants cannot.
Nested Tables versus Index-by Tables The Index-by tables and nested tables are just similar. For e.g. They have similar structure and their individual elements are accessed in
Defining REF CURSOR Types To make cursor variables, you take 2 steps. At first, you define a REF CURSOR type, and then declare the cursor variables of that type. You can defin
Ensuring Backward Compatibility The PL/SQL Version 2 permits some abnormal behavior which Version 8 disallows. Particularly, Version 2 permits you to (i) Make the forw
(a) What are decision support systems, and what role do they play in the business environment? (b) Data warehousing is defined as "a subject-oriented, integrated, non-volatile c
CLOSE Statement The CLOSE statement allows the resources held by a cursor variable or open cursor to be reused. No more rows can be fetched from the cursor variable or closed
CURRVAL and NEXTVAL The series is a schema object which generates the sequential numbers. Whenever you form a sequence, you can specify its primary value and an increment. T
THEO R Y OF PANSPERMIA - Arrhenius (1908) postulated the cosmic panspermia theory that claims that organisms existed throughout the universe, and their spores, etc., could
Negation (NOT, ¬) - SQL There are three rows instead of just two. As you can see, ¬ p is defined as in two-valued logic (2VL) when p is either true or false, but ¬ (unknown) i
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