Postgres Error: More than one row returned by a subquery used as an expression

Question

I have two separate databases. I am trying to update a column in one database to the values of a column from the other database:

UPDATE customer
SET customer         


        

Answer 1

The fundamental problem can often be simply solved by changing an = to IN, in cases where you've got a one-to-many relationship. For example, if you wanted to update or delete a bunch of accounts for a given customer:

WITH accounts_to_delete AS 
    ( 
        SELECT     account_id
        FROM       accounts a
        INNER JOIN customers c
                ON a.customer_id = c.id
        WHERE      c.customer_name='Some Customer'
    )

-- this fails if "Some Customer" has multiple accounts, but works if there's 1:
DELETE FROM accounts
 WHERE accounts.guid = 
( 
    SELECT account_id 
    FROM   accounts_to_delete 
);

-- this succeeds with any number of accounts:
DELETE FROM accounts
 WHERE accounts.guid IN   
( 
    SELECT account_id 
    FROM   accounts_to_delete 
);