SQL Update

Changing existing data with UPDATE

The UPDATE statement modifies data that is already in a table. You name the table, set one or more columns to new values, and use a WHERE clause to describe exactly which rows should change. Unlike INSERT, which creates new rows, UPDATE rewrites the values inside rows that already exist.

UPDATE Employees
SET department = 'Operations'
WHERE employee_id = 101;

This statement finds the single employee whose id is 101 and changes their department. The WHERE clause is what keeps the change limited to that one row.

Updating more than one column

You can change several columns in the same statement by separating the assignments with commas in the SET clause. Each assignment names a column and the new value it should hold.

UPDATE Employees
SET department = 'Engineering',
    salary = 75000
WHERE last_name = 'Okafor';

Basing new values on existing ones

The value on the right side of an assignment can be a calculation, and it may refer to the column's own current value. This is how you apply a raise, a discount, or any adjustment relative to what is already stored.

UPDATE Employees
SET salary = salary * 1.10
WHERE department = 'Sales';

How many rows will change?

The WHERE clause decides how many rows an update touches. A condition on a unique column changes one row, a broader condition changes many, and no condition at all changes them all. The table below shows the pattern.

• UPDATE changes values in rows that already exist.
• The SET clause can assign one or many columns.
• New values can be calculated from current values, such as salary * 1.10.
• Always include a WHERE clause unless you truly intend to change every row.