stock_transaction.amount * supply_rolls.weight_b / supply_rolls.weight)

CREATE OR ALTER TRIGGER WP_STOCK_TRANSACTION_BIU0 FOR WP_STOCK_TRANSACTION
ACTIVE BEFORE INSERT OR UPDATE POSITION 0
AS
declare variable weight numeric(15, 2);
declare variable weight_buh numeric(15, 2);
declare variable amount_use numeric(15, 2);
declare variable amount_buh numeric(15, 2);

BEGIN
  SELECT
    wp_supply_rolls.weight,
    CASE wp_paper.acc_in_buh
      WHEN 0 THEN wp_supply_rolls.weight_netto
      WHEN 1 THEN wp_supply_rolls.weight_brutto
    END weight_buh
  FROM
    wp_supply_rolls
  LEFT JOIN wp_paper ON wp_paper.id = wp_supply_rolls.paper
  WHERE
    wp_supply_rolls.id = new.roll_no
  INTO
    :weight,
    :weight_buh;


  IF (new.amount = :weight) THEN
    /* использовали рулон за раз*/
    new.amount_buh = weight_buh;
  ELSE BEGIN
    /* просуммируем движения по данному рулону*/
    SELECT
      sum(coalesce(wp_stock_transaction.amount, 0)),
      sum(coalesce(wp_stock_transaction.amount_buh, 0))
    FROM
      wp_stock_transaction
    WHERE
      wp_stock_transaction.roll_no = NEW.roll_no
    INTO
      :amount_use,
      :amount_buh;

    IF (:amount_use + new.amount = weight) THEN
      /* крайнее использование рулона*/
      /* вычислим остаток */
      new.amount_buh = weight_buh - amount_buh;
    ELSE
      /* посчитаем пропорциональный вес */
      new.amount_buh = new.amount * weight_buh / weight;
  END
END