sql - Oracle SQL 関数内で新しいパラメータの計算を行う方法

Question

Invoice テーブルにあるいくつかの値を使用して、この関数で未払い残高を計算しようとしています。計算線を正確にどこに配置すればよいかよくわかりません。どんな助けでも大歓迎です！

Create or Replace Function Get_balance_due(
f_invoice_id In Number)
Return Number
AS
    balance_due Number;
    f_invoice_total Number;
    f_payment_total Number;
    f_credit_total Number;


Begin
    select (vendor_id into f_vendor_id,
    invoice total into f_invoice_total,
    payment_total into f_payment_total,
    credit_total into f_credit_total)

From
    invoices
Where
    invoice_id = f_invoice_id
    balance_due = f_invoice_total - f_payment_total - f_credit_total;
Return (balance_due);
End;
/
SHOW ERRORS Function Get_balance_due;

Answer 1

このようにしてみて、

CREATE OR REPLACE 
FUNCTION get_balance_due(
         f_invoice_id IN NUMBER)
         RETURN NUMBER
AS
     balance_due NUMBER;
     f_invoice_total NUMBER;
     f_payment_total NUMBER;
     f_credit_total NUMBER;

BEGIN
     SELECT invoice total, payment_total, credit_total
     INTO  f_invoice_total, f_payment_total, f_credit_total
     FROM  invoices
     WHERE invoice_id = f_invoice_id;

     balance_due := f_invoice_total - f_payment_total - f_credit_total;

RETURN balance_due;
END;