I think what you mean is if you have a data set like this:

CREATE TABLE USERS ( TYPEID INT,USERNAME VARCHAR(30),)

INSERT VALUES (1,'JSMITH')

INSERT VALUES (2,'JDOE')

INSERT VALUES (1,'ASMITH')

and you do something like this:

UPDATE USERS

SET TYPEID = 3

WHERE TYPEID = 1

will the update statement update both JSMITH and ASMITH? The simple answer is yes, it will.