Poor performance of LAG function in view

Question

Hi,
I have a query, containing a LAG function, that runs supper fast. I've created a view based on the exact query but when I select from it the performance is very slow. If I exclude the column, that gets its value from the LAG function in the underlying query, the performance is the same as the original query. Does anybody know how I can get the view's performance to be the same as the query, and why the view is so much slower when it uses the exact same SQL as the query?
Many thanks,
Johan

Answer 1

Thanks Rob,
The sql in the view is not very complicated (I removed some of the columns to make it more readable). When I select all the columns from the view except prev_credit_balance the performance is great but when I add the prev_credit_balance column performance is slow. If I run the query from the create view statement below it is fast and include the LAG function. I do select from a rather large table (but then, why doesn't the query give the same problems as the view?)
CREATE OR REPLACE VIEW CALL_MONITOR_VIEW AS
select TT.Name Transaction_Type,
SUBSTR('27'||TD.Subscriber_UID,1,11) Msisdn,
TD.Subscriber_UID,
     IN_PLATFORM_PREFIX,
     TD.End_Of_Call,
     TD.Called_Party Other_Party,
     TD.Call_Duration,
     TD.Value,
(TD.Value*TT.Display_Sign) DISPLAY_VALUE,
     TD.Credit_Balance,
LAG(TD.credit_balance,1) over (order by TD.Subscriber_UID asc, TD.end_of_call asc) prev_credit_balance,
     TD.File_UID,
     TD.File_Type_UID,
     FT.Name File_Type
from Transaction_Detail TD,
Transaction_Type TT,
     File_Types FT,
     In_Platform ip,
TC_Unitization_Map UM
where TD.Transaction_Type_UID = TT.Transaction_Type_UID(+)
and TD.IN_PLATFORM_UID = IP.IN_PLATFORM_UID(+)
and TD.File_Type_Uid = FT.File_Type_uid
and TD.Provider_ID = UM.Provider_ID (+)
)