Hi folks,
We have an SQL type calculation view that is performing badly. Upon analyzing the visual plan we have found the root of the problem due to a case statement that is simply evaluating two tables and if a field is null in one table then choose the other alternate table field; something like this;
select
case when a.Customer IS NULL THEN
b.Customer
else
a.Customer
End
As TheCustomer
from table1 a join table2 b on a.XYZ = b.XYZ
etc
If we take the case statement away and simply return both values, the query runs very fast around 2 seconds. ie: something like this;
select
a.Customer as Customer1,
b.Customer as Customer2
from table1 a join table2 b on a.XYZ = b.XYZ
etc
But doing the case evaluation between the two field values bumps the execution time up to more than 60 seconds!
Has anybody experienced this and do you have any alternative suggestions to achieve this sort of thing? We have also tried doing a second pass and putting the case evaluation OUTSIDE the original select statement and there is some big improvement yet still not satisfactory. ie: something like this;
select
case when a.Customer IS NULL THEN
b.Customer
else
a.Customer
End
As TheCustomer from
( select
a.Customer as Customer1,
b.Customer as Customer2
from table1 a join table2 b on a.XYZ = b.XYZ
etc)
Thanks,
-Patrick