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Explain several types of constraints that can be specified using CREATE TABLE command. Explain CASCADE and RESTRICT clauses of DROP SCHEMA command?Constraint DescriptionPRIMARY 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).
Write short notes on extension and intension? In any data model, it is significant to distinguish among the description of the database and the database itself the description
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Niles Video Inc. wants to create a website for online sales of movies (DVD and videotapes). People will be allowed to register as customers on the website and to update their store
How many levels can be viewed in Architecture of the database ? Architecture of the database can be viewed as three levels.
Using the questions found at the end of Chapter 9 in your textbook, complete this homework activity. Students will submit a Word document answering questions 2, 3, and 4.
Describe in brief about DBMS ?
basic structure of xml
What do you understand by a view? What does WITH CHECK OPTION clause for a view do? - A view is a virtual table which comprises fields from one or more real tables. - It is
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