Informix SQL Update using an inner join

[cwbloucks]

I have a need to update 270,000 records with a particular flag. Using temporary tables and multiple update queries I have creating a staging table to put the original value and the new value. So the table structure is like this:

ID      ORIG_VALUE     NEW_VALUE
1223    A              B
1234    D              A
1334    ...

I'm struggling with creating an efficient UPDATE query that will update these records in mass.

In MS SQL I have used an INNER JOIN to accomplish this, but it seems that Informix doesn't support that. Right now I'm structuring the query like this:

UPDATE TABLEA
SET prod_field = (
  SELECT new_field
  FROM TABLEB_STAGING
  WHERE TABLEA.id = TABLEB_STAGING.id)

Is there a better way to accomplish this?

Thank you for any guidance!