Tunning SQL question

Hi Experts,
I have an access app linked to SQL BE, and using the following code as part of a dynamic build filter.
    If Not IsNull(Me.ComboSupervisor) Then
        sWhere = sWhere & " And PatientID in (Select id from Patients where supervisor = '" & ComboSupervisor & "')"
    End If
    If Not IsNull(Me.ComboCounty) Then
        sWhere = sWhere & " And PatientID in (Select id from Patients where County = '" & ComboCounty & "')"
    End If
    If Not IsNull(Me.ComboGender) Then
        sWhere = sWhere & " And PatientID in (Select id from Patients where Gender= '" & ComboGender & "')"
    End If

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Now I have the following questions re performance
1- would exists be a better choice than using in select?
2- if yes what is the correct sql syntax, I tried PatientID exists and didn't work?
3- Is it advisable to program that if user selects all 3 conditions they should all be included in one "in select" statement?
LVL 5
bfuchsAsked:
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Vitor MontalvãoMSSQL Senior EngineerCommented:
You can search all criteria in a single subselect:
    
If Not IsNull(Me.ComboSupervisor) Or Not IsNull(Me.ComboCounty) Or Not IsNull(Me.ComboGender) Then
    sWhere = sWhere & " And PatientID in (Select id from Patients where "
    sCriteria = ""
    If Not IsNull(Me.ComboSupervisor) Then
        sCriteria = "supervisor = '" & ComboSupervisor & "'"
    End If
    If Not IsNull(Me.ComboCounty) Then
        If sCriteria = "" Then
            sCriteria = sCriteria & "County = '" & ComboCounty & "'"
        Else
             sCriteria = sCriteria & " And County = '" & ComboCounty & "'"
        End If
    End If
    If Not IsNull(Me.ComboGender) Then
        If sCriteria = "" Then
            sCriteria = sCriteria & "Gender= '" & ComboGender & "'"
        Else
             sCriteria = sCriteria & " And Gender= '" & ComboGender & "'"
        End If
    End If
    sWhere = sWhere & sCriteria & ")"
End If

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Ammar GaffarSoftware EngineerCommented:
Post your select statement.
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bfuchsAuthor Commented:
Hi, here it goes.
SELECT PatientsOpenCases_HC.* FROM PatientsOpenCases_HC ORDER BY IIf([CoveredDate]=Date(),1,2), PatientsOpenCases_HC.StartDay, PatientsOpenCases_HC.CoveredDate;

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Vikas GargBusiness Intelligence DeveloperCommented:
Hi,

Exists  is always better than select if you are just doing join for filtering.
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PortletPaulfreelancerCommented:
Use a JOIN to the patients table, e.g.

SELECT PatientsOpenCases_HC.*
FROM PatientsOpenCases_HC
INNER JOIN Patients on PatientsOpenCases_HC.PatientID = Patients.ID
WHERE 

-- now add the required conditions
-- Patients.supervisor = '" & ComboSupervisor & "')"
-- Patients.County = '" & ComboCounty & "')"
-- Patients.Gender= '" & ComboGender & "')"

ORDER BY IIf([CoveredDate] = DATE (), 1, 2)
 , PatientsOpenCases_HC.StartDay
 , PatientsOpenCases_HC.CoveredDate;

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This should perform better than both IN() or EXISTS()
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Scott PletcherSenior DBACommented:
1.  Yes, EXISTS is better.
2.  Here's the general structure of an EXISTS WHERE condition:
     SELECT ...
     FROM outer_table ot
     WHERE EXISTS(SELECT 1 FROM Patients p WHERE p.id = ot.PatientID AND supervisor = ...)
or "county = ..." or whatever the other condition is.
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bfuchsAuthor Commented:
Hi Experts,
First thanks to all for replying.
@PortletPaul,
The problems I have with your suggestion is
1- this form is a continuous form where the top section is designated for filtering and the rest displays the data, the user selects a set of records they want to deal with, and then do all types of work, adding editing deleting etc, its not meant only for viewing.
2- I only copied one portion of the code building the filter string, however there are more parts, which some of them involves filtering for values in other tables, for example
    For Each v In Me.ListLanguages.ItemsSelected
        sin = sin & ",'" & Me.ListLanguages.ItemData(v) & "'"
    Next
    If Len(sin) > 0 Then
        sWhere = sWhere & " And PatientID in (Select PatientsID from PatientsLanguages_HC where language in (" & Mid(sin, 2) & "))"
        sin = ""
    End If

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how would I deal with all those, I cant be changing the base table join for each type of option user may select, or rather conjunction of types?

@Vitor Montalvão,
Something like that I had in my mind to apply, thanks for pre-designing it for me, however just wonder if that would make a difference on performance?

@Scott,
Thanks, I did that and so far in my testing it reduced up to 33% of the execution time.
this is what I currently have
If Not IsNull(Me.ComboSupervisor) Then
        sWhere = sWhere & " And exists (Select 1 from Patients where ID = PatientsOpenCases_HC.PatientID and supervisor = '" & ComboSupervisor & "')"
    End If
    If Not IsNull(Me.ComboCounty) Then
        sWhere = sWhere & " And exists (Select 1 from Patients where ID = PatientsOpenCases_HC.PatientID and County = '" & ComboCounty & "')"
    End If
    If Not IsNull(Me.ComboGender) Then
        sWhere = sWhere & " And exists (Select 1 from Patients where ID = PatientsOpenCases_HC.PatientID and Gender = '" & ComboGender & "')"
    End If

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Vitor MontalvãoMSSQL Senior EngineerCommented:
Something like that I had in my mind to apply, thanks for pre-designing it for me, however just wonder if that would make a difference on performance?
Yes, will make difference because you are going to perform a single subselect instead of 3 as you have now.
0
 
bfuchsAuthor Commented:
Hi Experts,
Before finalize this post I just want to double check if someone have a way I could make PortletPaul's suggestion work on my case, as this if possible would likely be the best option re performance?
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