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5. Domain Constraint: Domain Constraint allows you to specify a set of values that a particular attribute may take.
For example, attribute Gender has a domain constraint ensuring that it may take only two values, either M or F.
Similarly, we may constraint attribute Salary to take values within a reasonable range of numbers, say, between
8000 and 100000.
9.3 Structured Query Language (SQL)
Structured Query Language (SQL) is used to create and manipulate relational databases. It is a high-level interactive
language that allows users to specify what is required to be done in the form of queries. Unlike other high-level
languages, we do not need to specify how the SQL operations are implemented. Thus, SQL becomes an easy to learn
database language, so it is widely used. It efficiently manages large databases, provides fast responses to the queries
operating on data and facilitates an authentication mechanism that ensures the security of data.
SQL (Structured Query Language) offers a plethora of advantages that make it a fundamental and indispensable tool
for working with relational databases. Its simplicity and efficiency in data retrieval, management, and analysis make
it a top choice for businesses and developers alike. SQL excels at data retrieval, allowing users to formulate complex
queries to extract specific information from vast datasets quickly. It facilitates effective data management by enabling
the addition, modification, and deletion of records with ease while also enforcing data integrity through constraints,
ensuring the accuracy and consistency of stored information.
SQL: Most popular language for creating and manipulating relational databases.
Based on their functionality, SQL operations are organised in two categories, DDL (Data Definition Language) and DML
(Data Manipulation Language), as described below:
1. Data Definition Language (DDL): Data Definition Language (DDL) is used for describing database structure. It
is used to create and delete databases and tables. The attributes of already existing tables can also be added,
deleted or modified using DDL statements, also DDL commands. Some of the examples of DDL statements are
CREATE TABLE, ALTER TABLE, DROP TABLE, and TRUNCATE. In this chapter, we will discuss these in
detail.
DDL: Used for defining database attributes, their types, and constraints on attribute values.
2. Data Manipulation Language (DML): DML is used to retrieve and modify data. It includes statements that enable
us to store and retrieve information from database tables and modify the already stored data in the database. SQL
statements such as INSERT, SELECT, DELETE, and UPDATE are used for this purpose.
DML: Used to retrieve and modify data.
SQL also facilitates the creation of views containing the results produced by an SQL statement. Such saved results can
be used later.
9.4 Data Types
Attributes of a table describe the data that will be stored in the table. The data type indicates the domain of values for an
attribute. A data type may be of one of the several permissible types.
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