SQL update one column from another column in another table

Question

I read various post's prior to this. but none of them seemed to work for me.

As the title suggests, I am trying to update one column from a column in another table. I don't recall having problems with this before..

1. Table: user_settings.contact_id, I want to update with contacts.id where (user_settings.account_id == contacts_account_id)

2. Previously Contacts were linked to user accounts via the account_id. However, now we want to link a contact to user_settings via contacts.id

Below are a few examples of what I have tried, though none of them have worked. I would be interested in A.) Why they don't work and B.) What should I do instead.

Example A:

UPDATE user_settings
SET user_settings.contact_id = contacts.id 
FROM user_settings 
INNER JOIN contacts ON user_settings.account_id = contacts.account_id

Example B:

UPDATE (SELECT A.contact_id id1, B.id id2
  FROM user_settings A, contacts B
  WHERE user_settings.account_id = contacts.account_id)
SET id1 = id2

Example C:

UPDATE user_settings
SET user_settings.contact_id = (SELECT id
  FROM contacts
  WHERE (user_settings.account_id = contacts.account_id)
WHERE EXISTS ( user_settings.account_id = contacts.account_id )

I feel like my brain just shutdown on me and would appreciate any bumps to reboot it. Thanks :)

Answer 1

According to MySQL documentation, to do a cross table update, you can't use a join (like in other databases), but instead use a where clause:

http://dev.mysql.com/doc/refman/5.0/en/update.html

I think something like this should work:

UPDATE User_Settings, Contacts
    SET User_Settings.Contact_ID = Contacts.ID
    WHERE User_Settings.Account_ID = Contacts.Account_ID