Cascading updates question

I have two tables, Stock and Positions. Stock contains a Symbol column and a
Price column, and Symbol is the key. Positions contain the columns as well a
s
several other columns whose data should change with the Price. Positions can
have the same Symbol multiple times (it is keyed by Symbol-Account).
My design is to have a foreign key between the tables, so that when the
Price in the Stock column is updated, the Price in Positions also updates. I
am making some columns in the Positions table computed columns, so that they
recalculate when the Price updates.
My questions/concerns are:
1. Is this design any good? One alternative I was thinkning of was to use no
computed columns, and run a stored procedure frequently to update the
Positions.
2. Will the computed columns updated automatically when Price changes?
3. Will there be the possibility that some rows in Positions with the same
symbols are not updated simultaneously, so that the Price could be different
for the same symbol?
4. Do the rows lock while they are updating? This has implications because I
am querying this table often for other purposes.
5. If one computed column depends on another computed column, is there a way
to specify the order in which they calculate, or is this just a big no-no?
I am grateful for any insight.
Thank you,
CP Developer"CP Developer" <steved@.newsgroup.nospam> wrote in message
news:A40102EA-6AF1-4377-9332-09EFCAA83204@.microsoft.com...
>I have two tables, Stock and Positions. Stock contains a Symbol column and
>a
> Price column, and Symbol is the key. Positions contain the columns as well
> as
> several other columns whose data should change with the Price. Positions
> can
> have the same Symbol multiple times (it is keyed by Symbol-Account).
> My design is to have a foreign key between the tables, so that when the
> Price in the Stock column is updated, the Price in Positions also updates.
> I
> am making some columns in the Positions table computed columns, so that
> they
> recalculate when the Price updates.
> My questions/concerns are:
> 1. Is this design any good? One alternative I was thinkning of was to use
> no
> computed columns, and run a stored procedure frequently to update the
> Positions.
There are a few reasonable ways I can think of to have a comupted column
based on a column in a related table.
Put a phoney foreign key on (StockID, Price) and use cascade updates (your
idea).
Put a trigger on Stock to update the related positions.
Use a view to join the two tables and define the calculations there.

> 2. Will the computed columns updated automatically when Price changes?

> 3. Will there be the possibility that some rows in Positions with the same
> symbols are not updated simultaneously, so that the Price could be
> different
> for the same symbol?
No.

> 4. Do the rows lock while they are updating? This has implications because
> I
> am querying this table often for other purposes.
Yes. Make sure you have an index supporting the foreign key relationship.

> 5. If one computed column depends on another computed column, is there a
> way
> to specify the order in which they calculate, or is this just a big no-no?
>
No you cannot base one computed column on another. However you are free to
cut and paste the calculation for one column into the other.
Here's an example:
drop table position
drop table stock
go
create table stock
(
id int primary key,
price decimal(9,2),
constraint uk_id_price
unique (id,price)
)
create table position
(
account int not null, -- references account
stock int not null references stock,
price decimal(9,2) not null,
other_price as cast(price*.9 as decimal(9,2)),
constraint pk_position
primary key(account,stock),
constraint fk_position_stock_price
foreign key (stock,price)
references stock(id,price)
on update cascade
)
create index ix_position_stock_price
on position(stock,price)
go
insert into stock(id,price) values (1,3.50)
insert into position(account,stock,price) values (23,1,3.50)
go
update stock set price = 5.25 where id = 1
select * from position
David|||The columns will update when the price changes.
Create Table TableA
(
Symbol varchar(10),
Price Money,
Qty Int,
TotalCost As (Price * Qty)
)
Insert Into TableA
Select 'GBP', 14.52, 2
select * From TableA
Update TableA
Set Qty = 151, price = 45.65
select * From TableA
Drop table TableA
HTH
Barry|||I would store the price in one table only, and select it from there. If
you need you selects to be as fast as possible, consider using an
indexed view.