read_buch_tabelle <- function(conn){
  postings <- tbl(conn, "postings")
  entries  <- tbl(conn, "entries")
  accounts <- tbl(conn, "accounts")
  projects <- tbl(conn, "projects")
  contacts <- tbl(conn, "contacts")
  result <- postings |>
    left_join(entries,  by = c("entry_id" = "id")) |>
    left_join(contacts, by = c("contact_id" = "id")) |>  # contact_id jetzt verfügbar
    left_join(accounts, by = c("account_id" = "id")) |>
    left_join(projects, by = c("project_id" = "id")) |>
    select(id, valuta, konto, projektname, display_name,  amount, entry_id) |>
    collect() 
}

read_posting <- function(conn, id){
  dbxSelect(conn, paste0("SELECT * FROM postings WHERE id =", id))
}
read_postings_by_entry <- function(conn, id){
  dbxSelect(conn, paste0("SELECT * FROM postings WHERE entry_id =", id))
}