Class 12 DBMS and Structured Query Language Revision Notes

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 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.
Relation: Relation (collection of rows and columns) generally refers to an active entity on which we can perform various operations.
Database: Collection of logically related data along with its description is termed as database.
Tuple: A row in a relation is called a tuple.
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 key.
Alternate Key: All the candidate keys other than the primary keys 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
 Structured Query Language

SQL is a non procedural language that is used to create, manipulate and process the databases(relations).
1. Data Definition Language (DDL)
DDL contains commands that are used to create the tables, databases, indexes, views, sequences and synonyms etc.
e.g: Create table, create view, create index, alter table etc.



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