Cant Copy Data From One DB To Another.

I am trying to copy item names from one database to another if they share the same code number.
e.g.

UPDATE TABLE1
SET NAME = DB2.TABLE2.NAME
WHERE CODE = DB2.TABLE2.CODE

I dont know how to specify the second db as using a '.' here doesnt seem to work. I have also tried '..' and DB2.dbo.TABLE2 but get the same error - 'The column prefix 'Train_DB_FinancialsProd.dbo.ITEM_DEFINITIONS' does not match with a table name or alias name used in the query.'

I have checked that the spelling is ok so not sure why it doesnt work.


I have also tried using a temp db in between to copy the values across then try to update from the temp table but couldnt make that work either. e.g.

create table #tdhname
(
code char(50),
name char(100)
)


INSERT INTO #tdhname (code,name)
select distinct code,name from Train_DB_FinancialsProd..item_definitions tritm
where code = tritm.code
and tritm.ittyp_refno = 241

update pharmacy_items
set name = #tdhname.name <----- THIS DOESNT WORK
where #tdhname.code = code



Thanks!