How to optimize this query in SQL Server 2008 - sql

Question

How can I optimize query in SQL Server 2008?
Here is my Query.
SELECT DISTINCT
ListName ,
( SELECT COUNT(id)
FROM tbl_SurveyAssign
WHERE ListName = a.ListName
AND UserName IN (
SELECT UserName
FROM tbl_Panelist
WHERE tbl_Panelist.Subscribe = '1'
AND tbl_Panelist.Pending = '0'
AND tbl_Panelist.UserName IN (
SELECT UserName
FROM tbl_PanelistActivity
WHERE tbl_PanelistActivity.ActivityDate > ( GETDATE()
- 180 ) ) )
) AS Active ,
( SELECT COUNT(id)
FROM tbl_SurveyAssign
WHERE ListName = a.ListName
AND UserName IN (
SELECT UserName
FROM tbl_Panelist
WHERE tbl_Panelist.Subscribe = '1'
AND tbl_Panelist.Pending = '1' )
) AS Pending ,
( SELECT COUNT(id)
FROM tbl_SurveyAssign
WHERE ListName = a.ListName
AND UserName IN (
SELECT UserName
FROM tbl_Panelist
WHERE tbl_Panelist.Subscribe = '0'
AND tbl_Panelist.Pending = '0' )
) AS UnSubscribe ,
( SELECT COUNT(id)
FROM tbl_SurveyAssign
WHERE ListName = a.ListName
AND UserName IN (
SELECT UserName
FROM tbl_Panelist
WHERE tbl_Panelist.Subscribe = '1'
AND tbl_Panelist.Pending = '0'
AND tbl_Panelist.UserName NOT IN (
SELECT UserName
FROM tbl_PanelistActivity
WHERE tbl_PanelistActivity.ActivityDate > ( GETDATE()
- 180 ) ) )
) AS Inactive ,
( SELECT COUNT(id)
FROM tbl_SurveyAssign
WHERE ListName = a.ListName
) AS Total ,
( SELECT COUNT(id)
FROM tbl_SurveyAssign
WHERE ListName = a.ListName
AND UserName NOT IN ( SELECT UserName
FROM tbl_Panelist )
) AS NotMember
FROM tbl_SurveyAssign a

Answer 1

Without knowing the data, indexes etc and looking on the execution plan I would say there is two ways of making the query easier for the SQL server to process.
Simple soluiotn.
If you doing SQL queries inside the select part, the server is likely to make the same query for each row in tbl_SurveyAssign.
if you for each query making a query groped by listname and (select listname, count(*) from xxxxx group by listname) and joining in the result, the server just needs to makeing one query for each column. But it also depends if hte content of tbl_SurveyAssign always contains all list rows...
More advanced
At a quick glance it looks like you should be able to make this query with just one or two queries using joins. If you for exemple using tbl_SurveyAssign as a main table and to a left join with tbl_Panelist using username grouping on list name, you could do a count on tbl_PanelList you should get the number of members. From that you can calculate NotMembers but substracting form count(*) (this will skip a Not In( that is quite heavy.
Someting like this
select a.listname, count() Total, count() - count(b.username) NonMembers,
sum(case when b.Subscribe = '0' and b.Pending = '0' then 1 else 0 end) Unsubscribed,
sum(case when b.Subscribe = '1' and b.Pending = '1' then 1 else 0 end) Pending
from tbl_SurveyAssign a
left outer join tbl_PanelList b on a.username = b.username
You shold also be able to do a grouping query calculating the pending,active and unsubscribed just once.
if you grouping the activity by username and doing a max on the activity date you should be able to calculate the activity in one query as well.
select a.listname, count() Total, count() - count(b.username) NonMembers,
sum(case when b.Subscribe = '0' and b.Pending = '0' then 1 else 0 end) Unsubscribed,
sum(case when b.Subscribe = '1' and b.Pending = '1' then 1 else 0 end) Pending,
sum(case when b.Subscribe = '1' and b.Pending = '0' and act.DaysSinceLastActivity < 180 then 1 else 0 end) Active,
sum(case when b.Subscribe = '1' and b.Pending = '0' and act.DaysSinceLastActivity >= 180 then 1 else 0 end) Inactive
from tbl_SurveyAssign a
left outer join tbl_PanelList b on a.username = b.username
left outer join
(
select UserName, DateDiff(day, max(ActivityDate), GetDate()) DaysSinceLastActivity from tbl_PanelistActivity group by UserName
) act on a.username = act.username
Something like that. Keep in mind that its not tested in anyway, and I am quit sure I have misspelled a keyword or two.. But it will give you much less code.. and I think it is more readable as well. AND if there still is a performance issue, you will have a much smaller activity plan to dig in to...
I hope that helps you!