Update Query

Update Query in MySQL

Introduction

After inserting data into a table, you may need to modify existing records.

In MySQL, this is done using the UPDATE query.

The UPDATE statement allows you to change values in one or more columns for specific rows.

What is an UPDATE Query

The UPDATE statement is used to modify existing data in a table.

It does not create new rows — it only updates existing ones.

Basic Syntax

UPDATE table_name

SET column1 = value1, column2 = value2

WHERE condition;

Example

UPDATE Students

SET age = 21

WHERE id = 1;

This updates the age of the student with id = 1.

Update Multiple Columns

UPDATE Students

SET name = 'Rahul Sharma', age = 22

WHERE id = 1;

Update Multiple Rows

UPDATE Students

SET city = 'Delhi'

WHERE age > 20;

This updates all students with an age greater than 20.

Update All Rows

UPDATE Students

SET status = 'Active';

⚠️ This updates all rows in the table.

Using Conditions (WHERE)

The WHERE clause is very important.

Without WHERE:

• All rows will be updated
• Data may be changed unintentionally

Using Expressions in UPDATE

UPDATE Students

SET age = age + 1;

This increases the age for all students.

Using LIMIT

UPDATE Students

SET city = 'Mumbai'

LIMIT 2;

Updates only 2 rows.

Example Scenario

Suppose a student changes cities:

UPDATE Students

SET city = 'Bangalore'

WHERE id = 2;

Common Mistakes

• Forgetting WHERE clause
• Updating wrong rows
• Using incorrect column names
• Not testing queries before execution

Key Points to Remember

• UPDATE modifies existing data
• Always use WHERE for safety
• Can update single or multiple rows
• Supports expressions and conditions
• Changes are permanent