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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).
What is relational model feature? A relational model feature is much more data independence than some other database models.
Explain trigger? Trigger: A database trigger is procedural code which is automatically executed within response to certain events on a particular table in a database. Trigger
What are the objectives of query processing? Ans: The objectives of query processing is to transform a query written in a high level language into a accurate and efficien
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In problems 1 - 4, you are given the columns of a table, and a set of functional dependencies. Determine the normal form of this table. Remember that the normal form is the HIGHE
Define object-relational systems? Systems that give object-oriented extensions to relational systems are known as object-relational systems.
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Consider the relations EMPLOYEE(emp#, name) ASSIGNED_TO(project#, emp#) PROJECT(project#, project_name, chief) Express the subsequent queries in Relational Algebra (i) Ge
What are the advantages and disadvantages of merging an association into a class? Advantages: i) Less number of tables ii) Faster performance due to the fewer tables
Prove that a relation which is 4NF must be BCNF. Ans Let R be in 4NF. Suppose it is not in BCNF. Hence, there exists an FD X→Y in R such that x is not a super key. Although
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