sql statement conditions - asp.net

Question

I want to select all the Female patients from the patient table where the area = south or area= west and then group the result by Disease name
So I had to write the where condition like this :
command10.CommandText = "SELECT D.DiseaseName, COUNT(D.Patient_ID) AS PNO FROM PatientAffectDisease D INNER JOIN patient P on D.Patient_ID = P.Patient_ID WHERE P.Gender='" & "female" & "'" & " AND P.Area='" & "south" & " '" & "OR P.Area='" & "west" & " '" & " GROUP BY DiseaseName "
But this doesn't return the right result.
Any Idea?

Answer 1

Put parenthesis around your OR'd conditions
e.g.
WHERE P.Gender='" & "female" & "'" & " AND
(P.Area='" & "south" & " '" & "OR P.Area='" & "west" & " '" & ")
or just use an IN clause ...
where p.gender = 'female' and p.area in ('south', 'west')

Answer 2

The issue is that you had extra spaces after south and west with this code: " '"
You were trying to find 'south ' or 'west ', not 'south' or 'west'.
You can also modify this condition to use an IN clause.
command10.CommandText = "SELECT D.DiseaseName, COUNT(1) AS PNO FROM PatientAffectDisease D INNER JOIN patient P on D.Patient_ID = P.Patient_ID WHERE P.Gender='female' AND P.Area IN ('south', 'west') GROUP BY DiseaseName"

Answer 3

I think the problem is in your where clause specifically related to not using parentheses.
command10.CommandText =
"SELECT D.DiseaseName, COUNT(D.Patient_ID) AS PNO " & _
" FROM PatientAffectDisease D " & _
" INNER JOIN patient P on D.Patient_ID = P.Patient_ID " & _
" WHERE P.Gender='female' AND P.Area in ('south','west') " _
" GROUP BY DiseaseName "

Answer 4

Here is the text of your query:
SELECT
D.DiseaseName,
COUNT(D.Patient_ID) AS PNO
FROM PatientAffectDisease D
INNER JOIN patient P on D.Patient_ID = P.Patient_ID
WHERE P.Gender='female'
AND P.Area='south '
OR P.Area='west '
GROUP BY DiseaseName
In SQL, the AND naturally has precendence over the OR.
So you're effectively asking
WHERE (P.Gender='female' AND P.Area='south') OR (p.Area = 'west' )
You must use brackets to explicitly state the precedence you need
WHERE P.Gender='female' AND (P.Area='south' OR p.Area='west')

Answer 5

The reason your posted query isn't working properly is because you have an extra space after 'west' and 'south' in the generated query.
You should always group your logic with () to make it easier to maintain and understand the code - and keep away from bugs such as this one.
AND binds harder than OR, so what you had earlier was the same as writing:
(P.Gender = 'female' AND P.Area = 'west') OR P.Area = 'south' -- not correct
Instead of using P.Area = 'west' OR P.Area = 'south' you can use the IN operator, as in the below example:
SELECT D.DiseaseName, COUNT(D.Patient_ID) AS PNO
FROM PatientAffectDisease D
INNER JOIN patient P ON D.Patient_ID = P.Patient_ID
WHERE P.Gender = 'female' AND P.Area IN ('west','south')
GROUP BY D.DiseaseName
command10.CommandText = "SELECT D.DiseaseName, COUNT(D.Patient_ID) AS PNO FROM PatientAffectDisease D INNER JOIN patient P ON D.Patient_ID = P.Patient_ID WHERE P.Gender = 'female' AND P.Area IN ('west','south') GROUP BY D.DiseaseName"