在On语句中使用If语句

Question

I am presenting a summary of transactions by customer/account number. Transactions have two possible components, hardware or software I want the user to either get a presentation that has the total for the account, or hardware and software totals presented separately.

Currently the only option provided to the user is to get them separately. To accomplish this I have a subquery with a join whose on statement currently reads

on tb3.account_nbr=tb4.account_nbr and tb3.trans_type=tb4.trans_type

Eliminating the trans_type evaluation of the the statement returns the total for all transactions on an account.

I have added a checkbox on the form that indicates their preference for either getting the total or the two components separately. The resulting variable (@get_trans) value, is either "1" for show as separate totals by transaction type or "0" for summing all transaction types and showing as single total.

It would make sense that I could change the above to an if statement for the solution but it isn't working

on tb3.account_nbr=tb4.account_nbr and if(@get_trans=1,tb3.trans_type=tb4.trans_type,"")

Any help would be appreciated. Thanks, Jim

Answer 1

The problem is probably the else clause. The empty string will evaluate to 0 in this context -- and be treated as false. That causes the entire on condition to be false.

However, you can write the logic without the if :

on tb3.account_nbr = tb4.account_nbr and 
   (@get_trans <> 1 or tb3.trans_type = tb4.trans_type)

Note: this version assumes that @get_trans does not take on a NULL value. That is easily handled:

on tb3.account_nbr = tb4.account_nbr and 
   (@get_trans <> 1 or @get_trans is null or tb3.trans_type = tb4.trans_type)