SQL UPDATE

The UPDATE statement is used to change data in existing rows of a table.

🔹 Basic Syntax

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

⚠️ Always use a WHERE clause unless you want to update every row.

🔹 Example

-- Increase salary of employee with ID 101
UPDATE employees
SET salary = salary + 5000
WHERE employee_id = 101;

-- Update department for multiple employees
UPDATE employees
SET department = 'Finance'
WHERE department = 'Accounts';

🔹 Update All Rows (Be Careful!)

-- Set a default value for all rows
UPDATE employees
SET bonus = 0;

🔹 With Subqueries (Advanced)

-- Set manager name from another table
UPDATE employees e
SET manager_name = (
  SELECT name FROM managers m WHERE m.id = e.manager_id
)
WHERE EXISTS (
  SELECT 1 FROM managers m WHERE m.id = e.manager_id
);

🧠 Quick Recap

✅ Use UPDATE to modify your data precisely