如何创建一列作为其他列的总和的表？

Question

Create Table Billing3 
(
billingId int primary key,
FoodCharge float DEFAULT 0,
DoctorCharge float DEFAULT 0,
TestCharge float DEFAULT 0,
OperationCharge float DEFAULT 0,
RoomCharge float DEFAULT 0,
Total float DEFAULT (FoodCharge + DoctorCharge + TestCharge + OperationCharge + RoomCharge)
)

Answer 1

Alternatively, you can set up a MySQL insert trigger . But usually, you want to keep calculations in queries as you save on storage and avoid maintenance on a programming object. Plus, if one of the charges updates values, you would then need an update trigger.

USE `databasename`;
DELIMITER 
$$
CREATE TRIGGER `TotalCalculation` 
BEFORE INSERT 
ON `Billing3` FOR EACH ROW
-- Edit trigger body code below this line. Do not edit lines above this one
BEGIN
SET NEW.Total = NEW.FoodCharge + NEW.DoctorCharge + NEW.TestCharge +
                NEW.OperationCharge + NEW.RoomCharge;
END
$$

Answer 2

MySQL does not support calculated columns. You can use a view for this purpose:

create view v_billing3 as
    select b.*,
           (FoodCharge + DoctorCharge + TestCharge + OperationCharge + RoomCharge) as total
    from billing3 b;

Also, don't store numbers as floating points. Instead, use the fixed point type, decimal , for this purpose.