CBSE Class 12 Computer Science Dbms And Structured Query Language Worksheet

Basic Database concepts

Data : Raw facts and figures which are useful to an organization. We cannot take decisions on the basis of data.

Information: Well processed data is called information. We can take decisions on the basis of information Field: Set of characters that represents specific data element.

Record: Collection of fields is called a record. A record can have fields of different data types.

File: Collection of similar types of records is called a file.

Table: Collection of rows and columns that contains useful data/information is called a table. A table generally refers to the passive entity which is kept in secondary storage device.

Database: Collection of logically related data along with its description is termed as database.

Relation: Relation (collection of rows and columns) generally refers to an active entity on which we can perform various operations. It is also known as table.

Tuple: A row in a relation is called a tuple. It is also known as record.

Attribute: A column in a relation is called an attribute. It is also termed as field or data item.

Degree: Number of attributes in a relation is called degree of a relation.

Cardinality: Number of tuples in a relation is called cardinality of a relation.

Primary Key: Primary key is a key that can uniquely identifies the records/tuples in a relation. This key can never be duplicated and NULL.

Foreign Key: Non key attribute of a table acting as primary key in some other table is known as Foreign Key in its current table. This key is used to enforce referential integrity in RDBMS.

Candidate Key: Attributes of a table which can serve as a primary key are called candidate keys.

Alternate Key: All the candidate keys other than the primary key of a relation are alternate keys for a relation.

DBA: Data Base Administrator is a person (manager) that is responsible for defining the data base schema, setting security features in database, ensuring proper functioning of the data bases etc.

Select Operation: The select operation selects tuples from a relation which satisfy a given condition.

It is denoted by lowercase Greek Letter σ (sigma).

Project Operation:The project operation selects columns from a relation which satisfy a given condition. It is denoted by lowercase Greek Letter π (pi). It can be thought of as picking a sub set of all available columns.

Union Operation: The union (denoted as ∪) of a collection of relations is the set of all distinct tuples in the collection. It is a binary operation that needs two relations.

Set Difference Operation: This is denoted by – (minus) and is a binary operation. It results in a set of tuples that are in one relation but not in another

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