SQL UPDATE statement — How to Modify Existing Data in a Table

The SQL UPDATE Statement

The UPDATE statement changes the values of one or more columns in existing rows. You learned to add new data with INSERT INTO in the previous chapter — now you will learn to modify it. Here is the basic syntax:

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

• SET — specifies which columns to change and their new values
• WHERE — filters which rows to update (without it, ALL rows are updated)

We will use this Employees table:

+----+-----------+------------+--------+-----------+
| ID | Name      | Department | Salary | City      |
+----+-----------+------------+--------+-----------+
| 1  | Priya K.  | Sales      | 55000  | Mumbai    |
| 2  | John D.   | Marketing  | 62000  | London    |
| 3  | Arun M.   | IT         | 78000  | Delhi     |
| 4  | Emma W.   | Sales      | 51000  | Sydney    |
| 5  | Ravi S.   | IT         | 72000  | Mumbai    |
| 6  | Sara L.   | HR         | 58000  | New York  |
+----+-----------+------------+--------+-----------+

Update a Single Row

To update one specific row, use a WHERE clause that uniquely identifies it — typically by its primary key (ID):

UPDATE Employees
SET Salary = 60000
WHERE ID = 1;

+----+-----------+------------+--------+-----------+
| ID | Name      | Department | Salary | City      |
+----+-----------+------------+--------+-----------+
| 1  | Priya K.  | Sales      | 60000  | Mumbai    |
+----+-----------+------------+--------+-----------+
Priya's salary changed from 55000 to 60000.

Only the row where ID = 1 is affected. All other rows remain unchanged.

Update Multiple Columns at Once

You can change multiple columns in a single UPDATE statement by separating them with commas in the SET clause:

UPDATE Employees
SET Department = 'IT',
    City = 'Bangalore'
WHERE ID = 4;

+----+-----------+------------+--------+-----------+
| ID | Name      | Department | Salary | City      |
+----+-----------+------------+--------+-----------+
| 4  | Emma W.   | IT         | 51000  | Bangalore |
+----+-----------+------------+--------+-----------+
Emma moved from Sales/Sydney to IT/Bangalore.

Update Multiple Rows

When the WHERE clause matches more than one row, all matching rows are updated. You can combine conditions using AND, OR, NOT operators for precise targeting:

Give all IT employees a 10% raise:

UPDATE Employees
SET Salary = Salary * 1.10
WHERE Department = 'IT';

+----+-----------+------------+--------+-----------+
| ID | Name      | Department | Salary | City      |
+----+-----------+------------+--------+-----------+
| 3  | Arun M.   | IT         | 85800  | Delhi     |
| 5  | Ravi S.   | IT         | 79200  | Mumbai    |
+----+-----------+------------+--------+-----------+
Arun: 78000 → 85800 (+10%)
Ravi: 72000 → 79200 (+10%)

The expression Salary * 1.10 calculates a 10% increase based on the current salary for each row. SQL evaluates the expression row by row.

UPDATE Without WHERE — Danger Zone

-- ⚠️ This updates EVERY employee to Sales!
UPDATE Employees
SET Department = 'Sales';

Without WHERE, all 6 employees would be moved to Sales — destroying the original department data for IT, Marketing, and HR employees.

UPDATE with Calculations

You can use the current column value in your SET expression. SQL reads the old value and computes the new one:

Increase all salaries by 5000:

UPDATE Employees
SET Salary = Salary + 5000
WHERE City = 'Mumbai';

+----+-----------+------------+--------+-----------+
| ID | Name      | Department | Salary | City      |
+----+-----------+------------+--------+-----------+
| 1  | Priya K.  | Sales      | 60000  | Mumbai    |
| 5  | Ravi S.   | IT         | 77000  | Mumbai    |
+----+-----------+------------+--------+-----------+
Priya: 55000 → 60000 (+5000)
Ravi: 72000 → 77000 (+5000)

UPDATE with NULL Values

You can set a column to NULL to clear its value, or use IS NULL in the WHERE clause to update rows with missing data:

Clear Emma’s city:

UPDATE Employees
SET City = NULL
WHERE ID = 4;

Fill in missing departments:

UPDATE Employees
SET Department = 'General'
WHERE Department IS NULL;

This sets the department to “General” for any employee whose department is currently NULL.

Best Practices for SQL UPDATE

-- Step 1: Test with SELECT
SELECT * FROM Employees
WHERE Department = 'IT' AND Salary < 75000;

-- Step 2: If the correct rows are returned, run the UPDATE
UPDATE Employees
SET Salary = Salary + 3000
WHERE Department = 'IT' AND Salary < 75000;

For a complete reference of the UPDATE syntax, see the official MySQL UPDATE documentation. In the next chapter, you will learn how to remove rows entirely with SQL DELETE.

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UPDATE Employees
SET Department = 'Sales'
WHERE ID = 2;

UPDATE Employees
SET Salary = Salary + 2000
WHERE Department = 'Sales';

SELECT * FROM Employees
WHERE Department = 'Sales'
ORDER BY ID;

+----+-----------+------------+--------+-----------+
| ID | Name      | Department | Salary | City      |
+----+-----------+------------+--------+-----------+
| 1  | Priya K.  | Sales      | 57000  | Mumbai    |
| 2  | John D.   | Sales      | 64000  | London    |
| 4  | Emma W.   | Sales      | 53000  | Sydney    |
+----+-----------+------------+--------+-----------+

📖 Chapter 10 of 30 — SQL Tutorial on Neotech Navigators