Select statement where one of the column values change dynamically - sql

Question

I am trying to write a query as follows
select trading_day,trading_time,quantity,price from trade where trade_id=A903
Now for this trading_time the logic of extraction is
If the price above matches table trade_sb price and trade_id then that becomes trading time
if there is no match I go to another table trade_mb and search for match of price and trade_id
If there is no match in both above cases the original query holds good.
I tried with rank but couldn't get the result
Please help

Answer 1

it's not clear to me but i think you can create a function for it and use it in the query, see sample code below,
CREATE FUNCTION get_trading_time (p_trade_id VARCHAR2, p_price NUMBER, p_trading_time DATE) RETURN DATE
IS
v_trading_time DATE;
BEGIN
BEGIN
SELECT trading_time
INTO v_trading_time
FROM trade_sb
WHERE trade_id = p_trade_id
AND price = p_price;
RETURN v_trading_time;
EXCEPTION
WHEN NO_DATA_FOUND THEN NULL;
END;
BEGIN
SELECT trading_time
INTO v_trading_time
FROM trade_mb
WHERE trade_id = p_trade_id
AND prioe = p_price;
RETURN v_trading_time;
EXCEPTION
WHEN NO_DATA_FOUND THEN NULL;
END;
IF v_trading_time IS NULL THEN
RETURN p_trading_time;
END IF;
END;
/
select trading_day,trading_time,quantity,price ,
get_trading_time(trade_id, price, trading_time) trading_time2
from trade
where trade_id='A903';