hi all, i have this 2 table (there i simplify them)

Users
{
integer ID
}

Documents
{
integer ID,
integer USER_ID //it's a FK
timestamp CREATION_TIME
}

now i have this query

select u.ID from Users u

i need to modify that to have also the last document but i can change only the select statement, not the from ***,
so i think to write a procedure (it's pseudo-code)

integer GET_ID_OF_LAST_DOCUMENT_FOR_THIS_USER(integer userID)

and use a select as

select u.ID, GET_***_USER(u.ID) from User u

but i try a bit but it seems impossible, i'm right or exists same way to call a procedure in the 'SELECT ***' statement without change the 'FROM ***' ?