SQL: UPDATE Statement

The UPDATE statement allows you to update a single record or multiple records in a table.

The syntax for the UPDATE statement is:

  <code>  UPDATE table
    SET column = expression
    WHERE predicates;</code>


Example #1 - Simple example

Let's take a look at a very simple example.

   <code> UPDATE suppliers
    SET name = 'HP'
    WHERE name = 'IBM';</code>

This statement would update all supplier names in the suppliers table from IBM to HP.

Example #2 - More complex example

You can also perform more complicated updates.

You may wish to update records in one table based on values in another table. Since you can't list more than one table in the UPDATE statement, you can use the EXISTS clause.

For example:

 <code>   UPDATE suppliers    
    SET supplier_name =     ( SELECT customers.name
    FROM customers
    WHERE customers.customer_id = suppliers.supplier_id)
    WHERE EXISTS
      ( SELECT customers.name
        FROM customers
        WHERE customers.customer_id = suppliers.supplier_id);</code>

Whenever a supplier_id matched a customer_id value, the supplier_name would be overwritten to the customer name from the customers table.