While you can do this it is usually not a good idea. The main reason is
that now you have extra work somewhere (most likely a trigger) to keep that
value up to date and in some cases it can get out of sync. It is usually
better to simply issue a SUM or COUNT against the orders table with a WHERE
clause that filters by customer id. You would normally have an index on the
customer id and the operation would be pretty simple. If you use this value
a lot and there are not a large amount of new rows added to the Orders table
you might consider using an indexed view that sums up by customer. See more
in BOL on Indexed Views.

--
Andrew J. Kelly SQL MVP


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Hi,

I have two tables: table 1 contains customer information, and table 2
contains order information.

Table 2 is updated everytime a customer orders some goods. Therefore, a
customer, for example, can appear within table 2 on, say, a total of 5
occasions.

I would like a column in table 1 that tells me how many orders the
corresponding customer has placed in total. Is there anyway of linking
table 1 with table 2 to count the total number of orders a particular
customer has made? (i.e. in the above case 5)

Thanks for your time

Paul Evans