如何在创建表的约束或列级别内使用选择

Question

I have this table

ID | shares | value | percentage | total|
---------------------
1        2        60         0.222      270
2        4        120        0.444      270
3        3        90         0.333      270

I want to enter id and shares the remain column should be calculated automaticly where value is shares*30 and percentage is value divide total (value/total) and total is sum of all column value

I try computed columns but it does not work in total column

How can I do that?

Answer 1

You can declare some columns as Computed columns however the Total column is different, we need to create some Trigger to update that column:

create table mytable(
             ID int primary key,
             Shares int,
             Value as Shares * 30,
             Percentage as cast(cast(Shares * 30 as decimal)*100/Total as decimal(4,2)),
             Total int)
go
--create the trigger to update the Total column when any change is made on Shares
create trigger mytrigger on mytable 
for update, insert
as 
if update(Shares) 
   update mytable 
   set Total = (select sum(Value) from mytable)

Insert some data to test:

insert into mytable(ID,Shares) values(1,2)
insert into mytable(ID,Shares) values(2,4)
insert into mytable(ID,Shares) values(3,3)

Demo .