MySQL Advanced SUM function - mysql

Question

Good day!
I am sorry If this question was already asked, but I am kind of in hurry, so I am not sure.
I have 2 tables:
Table.Cars and Table.Price
In table Cars:
ID Auto_Increment Primary key NOT NULL
Name VARCHAR(30)
In table Price:
CarsID Primary key NOT NULL
Units Int
Price_per_unit decimal(10,2)
Total decimal(10,2)
So, what I need to do is, Create column (TOTAL* (Name does not need to be necessary this one)), in table Price, Set it to do Mathematical function.
Basicly, I want Column.Total to show Units * price_per_unit which would be:
ALTER TABLE Price
ADD TOTAL Decimal(10,2)
UPDATE Price SET Total = SUM(Units * Price_per_unit);
Which will look like this:
---------------------------------------------------
| ID | Units | Price_per_unit | Total | TOTAL |
---------------------------------------------------
| 1 | 12 | 30000,00 | 360000,00 | NULL |
| 2 | 5 | 12000,00 | 60000,00 | NULL |
And here comes my problem. I want to make TOTAL, to look like this:
---------------------------------------------------------
| ID | Units | Price_per_unit | Total | TOTAL |
---------------------------------------------------------
| 1 | 12 | 30000,00 | 360000,00 | 420000 |
| 2 | 5 | 12000,00 | 60000,00 | |
|_______________________________________________________|
So, next time, I put new record in table Price, I need TOTAL, to auto SUM my table by taking data from Units * Price_pre_unit.
So my question is, how do I make this query?

Answer 1

If you want Mysql database to do it automatically, it seems you are looking for a trigger. You should tun this code one time and the trigger will handle it for ever:
CREATE TRIGGER trigger_name
AFTER INSERT
ON price FOR EACH ROW
BEGIN
UPDATE Price SET Total = SUM(Units * Price_per_unit) where id=(select id from price order by id limit 1);
END;