Update table using query result - sql

Question

I am attempting to add the result of my query into the column of an existing table.
Thus far, the query below calculates the CAR_PRICE and displays the value. However, I want to add this value to the CAR_PAYMENT_TBL in the car_price column.
The create table commands below show the relevant table and the relationships between them. Is it possible to update the CAR_PRICE value in the CAR_PAYMENT_TBL?
SELECT C.TICKET_NO,
C.REG_ID,
C.BOOKING_ID,
(R.END_DATE-R.START_DATE) AS DAYS_STAYED,
(R.END_DATE-R.START_DATE)*5 AS CAR_PRICE
FROM CAR_TBL C
LEFT JOIN
ROOM_TBL R
ON C.BOOKING_ID = R.BOOKING_ID;
TABLE SCHEMA:
CREATE TABLE CAR_PAYMENT_TBL
(
TICKET_NO INT NOT NULL PRIMARY KEY,
CAR_PRICE NUMERIC(5,2)
);
CREATE TABLE CAR_TBL
(
REG_ID VARCHAR2(7) NOT NULL PRIMARY KEY,
TICKET_NO INT NOT NULL references CAR_PAYMENT_TBL(TICKET_NO),
BOOKING_ID INT NOT NULL references BOOKING_TBL(BOOKING_ID)
);
CREATE TABLE ROOM_TBL
(
STAY_NO INT NOT NULL PRIMARY KEY,
ROOM_NO VARCHAR2(4) NOT NULL references ROOM_DETAILS_TBL(ROOM_NO),
START_DATE DATE NOT NULL,
END_DATE DATE NOT NULL,
BOOKING_ID INT NOT NULL references BOOKING_TBL(BOOKING_ID)
);

Answer 1

You cannot reference other tables in an UPDATE statement in Oracle - use a subquery or a MERGE statement:
UPDATE CAR_PAYMENT_TBL
SET CAR_PRICE =
(select (ROOM_TBL.END_DATE - ROOM_TBL.START_DATE)*5 from room_tbl where ... )
WHERE CAR_PAYMENT_TBL.TICKET_NO = &TICKET_NO;
You'll also have to provide a sensible WHERE clause for the subquery (assuing &TICKET_NO is really a bind variable and not your join condition for the two tables).

Answer 2

If you want to update all the records of CAR_PAYMENT_TBL based on the values of ROOM_TBL
then
UPDATE CAR_PAYMENT_TBL
SET CAR_PRICE = (select (ROOM_TBL.END_DATE – ROOM_TBL.START_DATE)*5
FROM ROOM_TBL WHERE CAR_PAYMENT_TBL.TICKET_NO = ROOM_TBL.TICKET_NO)
If you want to update only specific record of CAR_PAYMENT_TBL then
UPDATE CAR_PAYMENT_TBL
SET CAR_PRICE = (select (ROOM_TBL.END_DATE – ROOM_TBL.START_DATE)*5
FROM ROOM_TBL WHERE CAR_PAYMENT_TBL.TICKET_NO = ROOM_TBL.TICKET_NO)
where CAR_PAYMENT_TBL = &ticket_num;