Computer Science By Mr. MRK
Delhi (2006)
5.a. What is an alternate key?
Ans. Alternate Key: A candidate key that is not the primary key is called an Alternate Key.
(Where Candidate Key: All attribute combinations inside a relation that can serve primary key
(uniquely identifies a row in a relation) are Candidate Keys as they are candidates for the primary key position.)
Outside Delhi 2006
5.a. What are DDL and DML?
Ans. DDL means Data Definition Language. DDL provides statements for the creation and deletion of tables and indexes. DML Means Data Manipulation Language. The DML provides statements to enter, update,delete data and perform complex queries on these tables. The SQL DDL(Data Definition Language) provides commands for defining relation schemas, deleting relations, creating indexes and modifying relation schemas. The SQL DML (Data Manipulation Language) includes a query language to insert, delete and modify tuples in the database. DML is used to put values and manipulate them in tables and other database objects and DDL is used to create tables and other database objects.
Delhi (2005)
5.a. What do you understand by the terms primary key and degree of a relation in relational data base?
Ans. Primary Key: A primary key is a set of one or more attributes that can uniquely identify tuples within the relations. The number of attributes in a relation is called Degree of a relation in relational data base.
Outside Delhi (2005)
5.a. What do you understand by the candidate key and cardinality of a relation in relational data base?
Ans. Candidate Key: All attribute combinations inside a relation that can serve as primary key(uniquely identifies a row in a relation) are Candidate Keys as they are candidates for the primary key position.The number of rows in a relation is known as cardinality of a relation.
2003
5.a. What is primary key in a table? (Define first normal form.- This is out of syllabus)
Ans. Primary Key: A primary key is a set of one or more attributes that can uniquely identify tuples within the relations.
2002
5.a. Differentiate between data definition language and data manipulation language.
Ans. The SQL DDL(Data Definition Language) provides commands for defining relation schemas, deleting relations, creating indexes and modifying relation schemas. The SQL DML (Data Manipulation Language) includes a query language to insert, delete and modify tuples in the database. DML is used to put values and manipulate them in tables and other database objects and DDL is used to create tables and other database objects.