Question

Can the update described below be completed in one UPDATE statement?

I want to update the Operators.name_id values with the Users.name_id values by joining on Users.name = Operators.op_name. Both Users.name and Operators.op_name are have a unique.

I know the situation described below doesn’t follow “best practices”, but it’s a much simpler example of what I’m trying to do: namely updating a field with the value from another joined table.

Table: Users
user_id    name
----------------
34         Billy
43         Jimmy
50         Joe

Table:  Operators (before UPDATE)
op_id   op_name   user_id
-------------------------
12      Billy     35
35      Jimmy     46
33      Joe       99


Table:  Operators (after UPDATE)
op_id   op_name   name_id
-------------------------
12      Billy     34
35      Jimmy     43
33      Joe       50

Answer 1

UPDATE   operators o
SET      user_id = 
         (
         SELECT  u.user_id
         FROM    users u
         WHERE   o.op_name = u.name
         )
WHERE    o.op_name IN
         (
         SELECT  name
         FROM    users
         )

In Oracle 10g, more efficient:

MERGE
INTO    operators o
USING   users u
ON      (u.name = o.op_name)
WHEN MATCHED THEN
UPDATE
SET     user_id = u.user_id