Explain cascade and restrict clauses of drop schema command, Database Management System

Assignment Help:

Explain several types of constraints that can be specified using CREATE TABLE command. Explain CASCADE and RESTRICT clauses of DROP SCHEMA command?

Constraint Description
PRIMARY KEY Determines that column(s) uniquely identifies each record. The primary key cannot be NULL, and the data value(s) must be unique.

FOREIGN KEY In a one-to-many relationship, the constraint is added to the "many" table. The constraint ensures which if a value is entered into a specified column, it must already exist in the "one" table, or the record is not added.

UNIQUE Ensures that all data values stored in a specified column are unique.
The UNIQUE constraint differs from the PRIMARY KEY constraint in which it permits NULL values.
CHECK Ensures in which a specified condition is true before the data value is added to a table. For example, an order's ship date cannot be previous than its order date.

NOT NULL Ensures in which a specified column cannon contain a NULL value. The NOT NULL constraint can just be created along with the column-level approach to table creation.

Prevents the DROP from taking place if any dependent objects exists (RESTRICT) or causes all dependent objects do also be dropped (CASCADE).


Related Discussions:- Explain cascade and restrict clauses of drop schema command

Define raid structure, Define raid? Briefly explain it? A range of disk...

Define raid? Briefly explain it? A range of disk organization methods, collectively called redundant arrays of independent disks (RAID) o   Improvement of reliability throug

Give short note on the following terms- dirty pages and etl, Give short not...

Give short note on the following terms:Dirty pages and ETL a.) Dirty pages. These are buffer pages which comprise modifications which haven't been written to disk. b.

What is theta join explain, What is theta join explain? Theta  Join  -...

What is theta join explain? Theta  Join  - The  theta  join  operation  is  an  extension  to  the  natural-join operation which permits us to merge selection and a Cartesian

Which model is record based logical model, Which model is record based logi...

Which model is record based logical model? Network Modelis basically known as record based logical model.

Difference between clustered and a non-clustered index, What are the differ...

What are the difference between clustered and a non-clustered index? A clustered index is a special type of index that reorders the way records in the table are physically stor

Lossless-join decomposition, Lossless-Join Decomposition   Let us sh...

Lossless-Join Decomposition   Let us show an intuitive decomposition of a relation. We require a better basis for deciding decompositions since intuition may not always be r

Define an operator that a relational algebra does not have, Define an opera...

Define an operator that a Relational Algebra does not have Ans: Relational Algebra does not have Aggregation operators.

Creating a view-data control, Creating a view: A query can be embed...

Creating a view: A query can be embedded within the CREATE VIEW STATEMENT A query can have complex select statements containing join, groups and sub- queries A quer

Objectives-transactions and concurrency management, Objectives After Re...

Objectives After Reading this part, you should be able to: Explain the term CONCURRENCY; Describe the term transaction and concurrent transactions; Talk about co

Give an example of operations from the state actions, Give an example of op...

Give an example of operations from the State Actions and Activities. For instance, in bank the activity verify account code and verify password

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