CREATE TABLE account
(
   id number(10) NOT NULL,
   account number(20) NOT NULL,
   CONSTRAINT account_id PRIMARY KEY (id)
);


CREATE TABLE account_statements
(
   id number(10) NOT NULL,
   account_id number(10) NOT NULL,
   statement_date date,
   inbalance number(20,2),
   outbalance number (20,2),
   CONSTRAINT statement_id PRIMARY KEY (id),
   CONSTRAINT account_statements_foreign_id FOREIGN KEY (account_id) REFERENCES account(id)
);


CREATE TABLE account_operations
(
   id number(10) NOT NULL,
   account_id number(10) NOT NULL,
   operdate date,
   summ number(20,2),
   opertype char(6),
   CONSTRAINT operations_id PRIMARY KEY (id),
   CONSTRAINT account_operations_foreign_id FOREIGN KEY (account_id) REFERENCES account(id)
);

CREATE OR REPLACE FUNCTION Get_debet_on_period (
   v_startdate IN date,
   v_enddate IN date,
   v_account IN account.account%TYPE)
RETURN number
IS
   v_debet_summ number(20,2);
BEGIN
   SELECT SUM(summ) INTO v_debet_summ
   FROM account_operations ao,
      account a
   WHERE ao.operdate between v_startdate AND v_enddate
      AND ao.opertype='DEBET'
      AND a.account=v_account
      AND ao.account_id=a.id;

    RETURN v_debet_summ;
END;

CREATE OR REPLACE FUNCTION Get_credit_on_period (
   v_startdate IN date,
   v_enddate IN date,
   v_account IN account.account%TYPE)
RETURN number
IS
   v_credit_summ number(20,2);
BEGIN
   SELECT SUM(summ) INTO v_credit_summ
   FROM account_operations ao,
      account a
   WHERE ao.operdate between v_startdate AND v_enddate
      AND ao.opertype='CREDIT'
      AND a.account=v_account
      AND ao.account_id=a.id;
    RETURN v_credit_summ;
END;

CREATE OR REPLACE FUNCTION Get_balance_on_date (
   v_date IN date,
   v_account IN account.account%TYPE)
RETURN number
IS
   v_balance_summ number(20,2);
   v_startdate date;
   v_startsumm number;
BEGIN
   SELECT MAX(as.statement_date) INTO v_startdate
   FROM account_statements as, account a
   WHERE a.id=as.account_id
   AND a.account=v_account
   AND as.statement_date<v_date;
   IF v_startdate IS NOT NULL THEN
      SELECT as.outbalance INTO v_startsumm
      FROM account_statement as, account a
      WHERE a.id=as.account_id
      AND a.account=v_account
      AND as.statement_date=v_statement_date;
      v_balance_summ:=v_startsumm+Get_credit_on_period(v_startdate, v_date, v_account)-Get_debet_on_period(v_startdate, v_date, v_account);
    ELSE
      v_startsumm:=0;
      v_balance_summ:=Get_credit_on_period(v_startdate, v_date, v_account)-Get_debet_on_period(v_startdate, v_date, v_account);
    END IF;

   RETURN v_balance_summ;
END;