The SQL to do this all in one go would be:
UPDATE TranslationMessage SET potemplate = NULL FROM POTMsgSet WHERE POTMsgSet.id = TranslationMessage.potmsgset AND POTMsgSet.potemplate <> TranslationMessage.potemplate;
The SQL to do this all in one go would be:
UPDATE TranslationMessage age.potmsgset AND potemplate <> TranslationMess age.potemplate;
SET potemplate = NULL
FROM POTMsgSet
WHERE
POTMsgSet.id = TranslationMess
POTMsgSet.