ALTER Command in SQL Explained in Detail | ADD, MODIFY, DROP, RENAME & Constraints with Examples
In this video, you will learn the ALTER Command in SQL with a complete practical and theoretical explanation.
The ALTER command is a DDL (Data Definition Language) statement used to change the structure of an existing table without deleting the table itself.
This video is perfect for students, beginners, interview preparation, exams, and database learners who want a clear understanding of how table structures can be modified after creation.
00:00 – Introduction to ALTER Command
00:37 – ADD (Add New Column)
01:59 – MODIFY TABLE
02:52 – RENAME COLUMN
03:33 – DROP COLUMN
04:23 – ADD & DROP CONSTRAINT
06:40 – RENAME TABLE
🔹 What You Will Learn in This Video
✔ What is the ALTER command in SQL
✔ Why ALTER is a DDL command
✔ Syntax and real-time examples
✔ Coding explanation with MySQL
✔ Important rules and characteristics
🔹 Topics Covered in Detail
🔸 1️⃣ ALTER TABLE ADD (Add New Column)
Purpose of ADD
Syntax explanation
Practical example
How existing rows behave
NULL and DEFAULT behavior
🔸 2️⃣ ALTER TABLE MODIFY (Change Column Definition)
Changing data type and size
Increasing vs decreasing column size
Risk of data loss
How existing data is handled
🔸 3️⃣ ALTER TABLE RENAME COLUMN (MySQL 8+)
Renaming columns safely
Effect on data and constraints
Syntax and example
🔸 4️⃣ ALTER TABLE DROP COLUMN
Permanently removing a column
Data deletion warning
Why DROP cannot be rolled back
🔸 5️⃣ ALTER TABLE ADD CONSTRAINT
Add PRIMARY KEY
Add UNIQUE constraint
Add FOREIGN KEY with parent–child relationship
Add CHECK constraint
Add DEFAULT value
Syntax and use cases
🔸 6️⃣ ALTER TABLE DROP CONSTRAINT
Drop PRIMARY KEY
Drop UNIQUE constraint
Drop FOREIGN KEY
Important MySQL-specific syntax
🔸 7️⃣ ALTER TABLE RENAME TABLE
Renaming an existing table
Syntax and example
When and why to use it
🔹 Important Characteristics of ALTER Command
✔ DDL Command (Auto-commit)
✔ Changes table structure, not records
✔ Cannot be rolled back
✔ Used after table creation
🎯 Who Should Watch This Video?
SQL beginners
Computer Science students
Exam & interview aspirants
MySQL learners
Anyone preparing for DBMS, SQL, or backend development
📘 Notes & Examples are explained step-by-step for easy understanding.
👍 If you find this video helpful, LIKE, SHARE, and SUBSCRIBE to the channel for more SQL tutorials, DBMS concepts, and MCQ shorts.
#ALTERCommand
#SQLAlter
#SQLTutorial
#DDLCommands
#SQLForBeginners
#MySQL
#DBMS
#SQLConstraints
#PrimaryKey
#ForeignKey
#UniqueConstraint
#CheckConstraint
#DefaultConstraint
#RenameColumn
#DropColumn
#AddColumn
#SQLWithExamples
#SQLInterviewQuestions
#ComputerScience
#ProgrammingTutorial
#DatabaseManagement
#LearnSQL
#SQLCoding