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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).
Which operation is used if we are interested in only certain columns of a table? PROJECTION operation is used if we are interested in only certain columns of a table.
Explain the difference between the three storage types - volatile, non volatile and stable. Ans: Volatile storage: if storage media loses data while power goes off,
What is relationship instance ? Relationship Instance - A relationship is a relation between two or more entities. An instance of relationship set is a set of relationships.
Explain how you can define an object model of a system. A list of terms that shall be used by end users to describe state and behaviour of objects in system. Different use
Describe identifying relationship? Identifying relationship: It is relationship among strong entity and a weak entity it is represented through a doubly outlined diamond in C
Mention the several levels in security measures. A) Database system B) Operating system C) Network D) Physical Human
For the relations answer the following queries in SQL Street (name, location, city) House (number, street_name) Lives (name, house_number) (i) Obtain the names of persons who liv
What is the main advantage of the object model? What are its different components? The object model focuses on the logical data structures. Each object model comprises of many
To eliminate duplicate rows (distinct operator) Example: SELECT DISTINCT DEPTNO FROM EMP;
how does Btree differ from a B+ - tree?
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