Basic SQL Commands

Basic SQL Commands (CRUD Operations)

Now that you understand:

• How to create databases and tables
• Data types
• Constraints

It’s time to learn how to work with data inside tables.

This is where SQL becomes powerful.

1. What is SQL?

SQL (Structured Query Language) is a language used to communicate with relational databases.

In MySQL, SQL is used to:

• Create data
• Read data
• Update data
• Delete data

These four operations are called CRUD operations:

Letter	Meaning	SQL Command
C	Create	INSERT
R	Read	SELECT
U	Update	UPDATE
D	Delete	DELETE

These are the foundations of database programming.

2. SELECT – Reading Data

The SELECT statement is used to retrieve data from a table.

Basic Syntax

SELECT column_name FROM table_name;

Example

SELECT name FROM Students;

This retrieves only the name column.

Selecting All Columns

SELECT * FROM Students;

* means all columns.

3. INSERT – Adding Data

The INSERT statement is used to add new records.

Syntax

INSERT INTO table_name (column1, column2)

VALUES (value1, value2);

Example

INSERT INTO Students (id, name, age)

VALUES (1, 'Rahul', 20);

Inserting Multiple Rows

INSERT INTO Students (id, name, age)

VALUES

(2, 'Anita', 21),

(3, 'Aman', 19);

Important:
Always match column order with values.

4. UPDATE – Modifying Data

The UPDATE statement changes existing data.

Syntax

UPDATE table_name

SET column_name = value

WHERE condition;

Example

UPDATE Students

SET age = 22

WHERE id = 1;

This updates only the student with id = 1.

⚠ Important:
If you forget the WHERE clause:

UPDATE Students SET age = 22;

This updates all rows.

Always use WHERE carefully.

5. DELETE – Removing Data

The DELETE statement removes records.

Syntax

DELETE FROM table_name

WHERE condition;

Example

DELETE FROM Students

WHERE id = 3;

This deletes only the student with id = 3.

⚠ Warning:
If you write:

DELETE FROM Students;

All rows will be deleted.

6. WHERE Clause – Filtering Data

The WHERE clause is used to filter records.

Example

SELECT * FROM Students

WHERE age > 20;

This shows students older than 20.

Common Operators

Operator	Meaning
=	Equal
>	Greater than
<	Less than
>=	Greater than or equal
<=	Less than or equal
!=	Not equal

Example:

SELECT * FROM Students

WHERE name = 'Rahul';

WHERE makes queries powerful because it allows condition-based filtering.

7. LIMIT & OFFSET

These are used to control how many rows are returned.

LIMIT

SELECT * FROM Students

LIMIT 5;

This returns only 5 rows.

OFFSET

SELECT * FROM Students

LIMIT 5 OFFSET 5;

This skips the first 5 rows and returns the next 5.

Used for:

• Pagination
• Large datasets
• Displaying limited results

8. Writing Readable SQL Queries

Good SQL is not just correct — it should be readable.

1. Use Proper Formatting

Bad:

select * from students where age>20;

Good:

SELECT *

FROM Students

WHERE age > 20;

2. Use Meaningful Column Names

Avoid:

• col1
• data1

Use:

• student_name
• date_of_birth

3. Write Keywords in Uppercase

Common convention:

• SELECT
• INSERT
• UPDATE
• DELETE
• WHERE
• LIMIT

This improves clarity.

4. Add Comments

-- Get students older than 20

SELECT * FROM Students

WHERE age > 20;

Readable SQL is easier to debug and maintain.

Final Summary

Basic SQL commands allow you to perform CRUD operations:

• SELECT → Read data
• INSERT → Add data
• UPDATE → Modify data
• DELETE → Remove data

The WHERE clause filters data.
LIMIT & OFFSET control the number of results.