Another way to select a value (or multiple values) for an update is to use a scalar-subselect. The scalar-subselect allows you to update one or more columns by setting them to one or more values selected from another table.
In the following example, an employee moves to a different department but continues working on the same projects. The employee table has already been updated to contain the new department number. Now the project table needs to be updated to reflect the new department number of this employee (employee number is '000030').
UPDATE PROJECT
SET DEPTNO =
(SELECT WORKDEPT FROM EMPLOYEE
WHERE PROJECT.RESPEMP = EMPLOYEE.EMPNO)
WHERE RESPEMP='000030'
This same technique can be used to update a list of columns with multiple values returned from a single select.