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

Database backup, Discuss the importance and characteristics of database bac...

Discuss the importance and characteristics of database backup and recovery procedures, then describe the actions that must be detailed in backup and recovery plan

Determine candidate and primary key, A video rental company has several bra...

A video rental company has several branches. The data held on each branch is the branch address made up of street, city, state, and zip code, and the telephone number. Ea

List the data structures implemented by the storage manager, List the data ...

List the data structures implemented by the storage manager. The storage manager executes the following data structure a) Data files b) Data dictionary c) indices

What is completeness constraint on generalization, What is completeness con...

What is completeness constraint on generalization? Define the variation between total and partial design constraint. Give an example each.       Ans: Completeness Constraints

Organic compounds, #question.explain diversity and magnitude of organic com...

#question.explain diversity and magnitude of organic compounds and general properties?

Function module, When a function module is activated syntax checking is per...

When a function module is activated syntax checking is performed automatically. YEs, a function module is activated syntax checking.

What is a disjoint less constraint, What is a disjoint less constraint? ...

What is a disjoint less constraint? Ans: It needs that an entity belongs to no much more than one level entity set.  Disjoint less constraint needs that an entity belongs to

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