UPDATE — Modify Existing Data

The UPDATE statement allows you to change existing data in a table.
You can update one column, multiple columns, or entire rows.

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Syntax

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

Important: Always use a WHERE clause unless you want to update all rows.

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Example 1: Update One Column

UPDATE employees
SET age = 30
WHERE id = 1;

This changes the age of the employee with id = 1 to 30.

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Example 2: Update Multiple Columns

UPDATE employees
SET department = 'Sales', age = 34
WHERE name = 'Thomas';

This updates both department and age for the employee named 'Thomas'.

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Common Mistakes

Forgetting the WHERE clause

UPDATE employees
SET age = 30;

Mistake: This will update age = 30 for all employees, which is probably not what you want.

Tip: Always include a WHERE condition to target specific rows:

UPDATE employees
SET age = 30
WHERE id = 1;