SQL UPDATE Statement - Modifying Data in SQL Tables

Introduction

Databases are living systems — they evolve. Students change addresses, classes get updated, mistakes are corrected. The UPDATE statement is your tool to reflect these changes without deleting and reinserting data.

Syntax of UPDATE Statement

UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;

Where:

• table_name: The name of the table you want to update
• SET: Specifies which columns should be updated and their new values
• WHERE: Filters which rows to update (always use this carefully!)

SQL UPDATE Example – Changing a City

Consider that we have students table in our database.

CREATE TABLE students (
  roll_no INT PRIMARY KEY,
  name VARCHAR(50),
  class VARCHAR(10),
  age INT,
  city VARCHAR(30)
);

INSERT INTO students VALUES
(1, 'Arjun Deshmukh', '10A', 15, 'Pune'),
(2, 'Priya Reddy', '9B', 14, 'Hyderabad'),
(3, 'Karan Mehta', '10A', 15, 'Ahmedabad');

roll_no	name	class	age	city
1	Arjun Deshmukh	10A	15	Pune
2	Priya Reddy	9B	14	Hyderabad
3	Karan Mehta	10A	15	Ahmedabad

Suppose Karan moved from Ahmedabad to Surat. Let’s update his city:

UPDATE students
SET city = 'Surat'
WHERE roll_no = 3;

Table Contents after UPDATE

SELECT * FROM students;

roll_no	name	class	age	city
1	Arjun Deshmukh	10A	15	Pune
2	Priya Reddy	9B	14	Hyderabad
3	Karan Mehta	10A	15	Surat

Updating Multiple Columns

Let’s say Priya changed class and city:

UPDATE students
SET class = '10C', city = 'Bengaluru'
WHERE roll_no = 2;

Table Contents after UPDATE

SELECT * FROM students;

roll_no	name	class	age	city
1	Arjun Deshmukh	10A	15	Pune
2	Priya Reddy	10C	14	Bengaluru
3	Karan Mehta	10A	15	Surat

UPDATE All Rows (Without WHERE)

This is powerful — and dangerous. Without a WHERE clause, all rows are updated.

UPDATE students
SET age = age + 1;

Table Contents after UPDATE

SELECT * FROM students;

roll_no	name	class	age	city
1	Arjun Deshmukh	10A	16	Pune
2	Priya Reddy	10C	15	Bengaluru
3	Karan Mehta	10A	16	Surat

UPDATE Using Conditions – WHERE with AND

Update students of class 10A who live in Pune:

UPDATE students
SET city = 'Mumbai'
WHERE class = '10A' AND city = 'Pune';

WHERE condition selects all the rows with class 10A and place Pune.

roll_no	name	class	age	city
1	Arjun Deshmukh	10A	16	Pune
2	Priya Reddy	10C	15	Bengaluru
3	Karan Mehta	10A	16	Surat

Table Contents after UPDATE

SELECT * FROM students;

roll_no	name	class	age	city
1	Arjun Deshmukh	10A	16	Mumbai
2	Priya Reddy	10C	15	Bengaluru
3	Karan Mehta	10A	16	Surat

SELECT * FROM students
WHERE class = '10A' AND city = 'Pune';

Using UPDATE with Calculations

Let’s assume we have a student_marks table:

CREATE TABLE student_marks (
  roll_no INT,
  subject VARCHAR(30),
  marks INT
);

INSERT INTO student_marks VALUES
(1, 'Maths', 80),
(2, 'Maths', 85),
(3, 'Maths', 75);

roll_no	subject	marks
1	Maths	80
2	Maths	85
3	Maths	75

Add 5 bonus marks to everyone:

UPDATE student_marks
SET marks = marks + 5;

roll_no	subject	marks
1	Maths	85
2	Maths	90
3	Maths	80

Best Practices

• Use WHERE thoughtfully — it's your safety net.
• Preview with SELECT to see what rows will change.
• Back up your data before bulk updates in production.

Summary

The UPDATE statement lets your database grow and adapt. Whether you're correcting errors, migrating students to a new class, or applying performance bonuses — this is how you make your tables dynamic and relevant.