-----------------------------------------------------------------------------------------------------------
SQL (Structured Query
Language) is used to create, manage, secure,
and retrieve data from a database.
SQL is divided
into 4 main components:
1. DDL
(Data Definition Language)
2. DML
(Data Manipulation Language)
3. DCL
(Data Control Language)
4. DQL
(Data Query Language)
1. DDL (Data Definition Language)
DDL is used to create and modify the structure of database objects such as tables, views, and indexes.
Simple Definition
DDL is used to create, change, or delete
database structures.
Common Commands
- CREATE
- ALTER
- DROP
- TRUNCATE
- RENAME
Practical Example
Create a Table
CREATE TABLE Student
(
StudentID NUMBER,
StudentName VARCHAR2(30),
City VARCHAR2(20)
);
Output
Table Created.
Add a New Column
ALTER TABLE Student
ADD Email VARCHAR2(50);
Delete the Table
DROP TABLE Student;
Real-Life Example
Think of
building a new classroom.
- Construct classroom → CREATE
- Add windows → ALTER
- Remove classroom → DROP
2. DML (Data Manipulation Language)
DML is used to insert, update, and delete data inside a table.
Simple Definition
DML changes the data stored in tables.
Common Commands
- INSERT
- UPDATE
- DELETE
Practical Example
Insert Data
INSERT INTO Student VALUES(101,'Rahul','Ahmedabad');
Update Data
UPDATE Student
SET City='Surat'
WHERE StudentID=101;
Delete Data
DELETE FROM Student
WHERE StudentID=101;
Real-Life Example
Student
admission office
- New admission → INSERT
- Change address → UPDATE
- Cancel admission → DELETE
3. DCL (Data Control Language)
DCL is used to give or remove permissions from users.
Simple Definition
DCL controls who can access the database.
Common Commands
- GRANT
- REVOKE
Practical Example
Give Permission
GRANT SELECT
ON Student TO Rahul;
Rahul can now view the
Student table.
Remove Permission
REVOKE SELECT
ON Student FROM Rahul;
Rahul can no longer view the
Student table.
Real-Life Example
College
Library
- Give library card → GRANT
- Cancel library card → REVOKE
4. DQL (Data Query Language)
DQL is used to retrieve data from the database.
Simple Definition
DQL is used to view or search data stored
in tables.
Common Command
- SELECT
Practical Example
View All Records
SELECT * FROM Student;
View Specific Columns
SELECT StudentName, City FROM Student;
Search Data
SELECT *
FROM Student
WHERE City='Ahmedabad';
Real-Life Example
Searching a
student's result.
You are not changing
anything.
You are only viewing the
information.
Simple Database Example
Suppose we have this table:
Student Table
|
StudentID |
Name |
City |
|
101 |
Rahul |
Ahmedabad |
|
102 |
Priya |
Surat |
DDL Example
CREATE TABLE Student(...);
Creates the table.
DML Example
INSERT INTO Student
VALUES(103,'Amit','Rajkot');
Adds a new student.
DQL Example
SELECT * FROM Student;
Displays all students.
DCL Example
GRANT SELECT
ON Student TO User1;
Allows User1 to view the
table.
Difference Between DDL, DML, DCL and DQL
|
Feature |
DDL |
DML |
DCL |
DQL |
|
Full
Form |
Data Definition Language |
Data Manipulation Language |
Data Control Language |
Data Query Language |
|
Purpose |
Create or modify database
structure |
Insert, update, delete
data |
Manage user permissions |
Retrieve data |
|
Works
On |
Database objects (tables,
views, indexes) |
Data inside tables |
Users and privileges |
Data inside tables |
|
Main
Commands |
CREATE, ALTER, DROP,
TRUNCATE, RENAME |
INSERT, UPDATE, DELETE |
GRANT, REVOKE |
SELECT |
|
Changes
Structure? |
✅ Yes |
❌ No |
❌ No |
❌ No |
|
Changes
Data? |
❌ No |
✅ Yes |
❌ No |
❌ No |
|
Retrieves
Data? |
❌ No |
❌ No |
❌ No |
✅ Yes |
|
Security
Related? |
❌ No |
❌ No |
✅ Yes |
❌ No |
Memory Trick
|
Component |
Easy Memory |
|
DDL |
Design the database (Create the structure) |
|
DML |
Manage the data (Insert, Update, Delete) |
|
DCL |
Control user access (Grant, Revoke) |
|
DQL |
Query the data (Select/View) |
Summary
- DDL → Defines the structure of the database
(e.g., CREATE TABLE).
- DML → Manipulates the data stored in tables
(e.g., INSERT, UPDATE, DELETE).
- DCL → Controls user permissions and
security (e.g., GRANT, REVOKE).
- DQL → Retrieves and displays data from the
database (e.g., SELECT).
These four SQL components work together to build, manage, secure, and query a relational database effectively.
Or follow my blog from the below link
){kind=link}
0 Comments