SQL Data Definition Language


SQL Tutorial 5: Data Definition Language

SQL (Structured Query Language) is for Database Developers, Database Administrators, and Database testers.

Three main subsets of SQL:

i) Data Definition Language
ii) Data Manipulation Language
iii) Data Control Language
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Database Engine is required to practice / use SQL, we can use any Database engine like Oracle, MS SQL Server or MySQL etc...
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Overview

i) Database Management System
ii) Database Engine
iii) Database Server
iv) Database
v) Table and Record

i) Database Management System

> Database Management System is designed to allow the definition, creation, querying, update and administration of Databases

> It is a Computer Software Application that interacts with the user, other applications, and the database itself to capture and analyze the data

ii) Database Engine

Software that stores and retrieves data in a database. It may be self-contained program or the part of DBMS that performs the storage and retrieval operations.

iii) Database Server

Database Management Systems provide Database server functionality, database server provides database services to other computer programs or computers.

iv) Database


> A Database is a Systematic collection of data
> Databases support storage and manipulations of data
> Databases make data management easy

v) Table and Record

> A Table is a predefined format of rows and columns that define an entity
> Each column contains a different type of attribute and each row corresponds a single record.
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Data Definition Language

Data Definition Language Commands are used to Create, Modify, and Drop the Structure of Database Objects like Table, View, and Index etc...

Data Definition Language Commands and Operations
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Important DDL Commands

1) Create
2) Alter
3) Drop
4) Truncate
5) Rename
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Important DDL Operations

1) Create a Database
2) Use Database
3) Rename a Database
4) Drop Database
5) Create a Table
6) Rename Table
7) Add a Column to exiting Table
8) Add multiple columns to existing Table
9) Modify an existing column
10) Rename a Column
11) Drop a Column
12) Truncate a Table
13) Drop a Table
SQL Tutorial
Download and Install MS SQL Server Express Edition (It is Free Edition) and practice SQL Commands and Operations.
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1) Create a Database

Syntax:

Create Database databaseName;

Example:

Create Database gcreddyDB;
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2) Use Database

Syntax

Use databaseName;

Example:

Use gcreddyDB;
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3) Rename a Database

Syntax

Alter Database databaseName Modify Name = newdatabseName;

Example:

Alter Database gcreddyDB Modify Name = hyderabad

Or

Alter Database gcreddyDB 
Modify Name = hyderabad
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4) Drop a Database

Syntax:

Drop Database databaseName;

Example:

Drop Database gcreddyDB;
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5) Create a Table

Syntax:

Create Table tableName
(
column1_name dataType(size),
column2_name dataType(size),
.
.
.
);

Example:

Create Table Students
(
STID int,
STName char(50),
);
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View Table info
Select * from Students

View Table Schema
Select * from INFORMATION_SCHEMA.COLUMNS where TABLE_NAME = 'Students';
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6) Rename Table

Syntax:

EXEC sp_rename 'old_tablename', 'new_tablename';

Example:

EXEC sp_rename 'Students', 'newStudents';
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7) Add a Column to existing Table

Syntax:

Alter Table table_name add column_name dataType(size);

Example:
Alter Table newStudents add City char(50);
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8) Add multiple columns to an existing Table

Syntax:

Alter Table table_name add column1_name dataType(size), column2_name dataType(size);

Or
Alter Table table_name add
column1_name dataType(size),
column2_name dataType(size),
.
.;

Example:

Alter Table newStudents add add1 char(100), add2 char(70);

Or

Alter Table newStudents add 
add3 char(100), 
add4 char(70),
add5 char (100),
phone int;
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9) Modify an existing column

Syntax: 

Alter Table table_name Alter Column column_name dataType(size);

Example:

Alter Table newStudents Alter Column add1 varchar(150);
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10) Rename a Column

Syntax:

EXEC sp_rename 'table_name.old_column_name', 'new_colum_name';

Example:
ExEC sp_rename 'newStudents.phone', 'mobile'
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11) Drop a Column

Syntax:

Alter Table table_name Drop Column column_name;

Example:

Alter Table newStudents Drop Column City;
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12) Truncate a Table

Truncate Table command is used to delete complete data from an existing table

Syntax:

Truncate Table table_name;

Example:

Truncate Table newStudents;
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13) Drop a Table

Drop Table command is used to delete complete Table (Data and Table Structure) from the Database.

Syntax:

Drop Table table_name;

Example:
Drop Table newStudents;
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Also Read:


1) SQL Tutorial 1: Introduction to SQL

2) SQL Tutorial 2: SQL Overview


3) SQL Tutorial 3: MS SQL Server Installation


4) SQL Tutorial 4: Database Fundamentals, SQL Elements


SQL Interview Questions and Answers

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