How to join additional table when left outer not working - sql-server

Question

I have an existing proc which I have chopped up for brevity's sake
SELECT col1, col2
FROM (
col1, col2
SELECT col3--aggregate columns
FROM iep i
INNER JOIN student s ON s.studentID = i.studentID
INNER JOIN dbo.IDuration id ON i.IepID = id.iepID
INNER JOIN AppointmentStudent as ON s.studentID = as.studentID
INNER JOIN Appointment a ON as.appointmentID = a.appointmentID
INNER JOIN AppointmentTherapist at ON a.appointmentID = at.appointmentID
WHERE s.studentID = #studentID
GROUP BY col1, col2
) t
The aggregate columns summarizes appointments into the weeks of the year, but it only does sos for the weeks the student had appointments. I have an additional table called SchoolWeekYear that is populated with all of the weeks of the year that I am trying to integrate to this proc so I get 52 records back and not just the handful I am currently getting.
SELECT col1, col2
FROM (
col1, col2
SELECT col3--aggregate columns
FROM iep i
INNER JOIN student s ON s.studentID = i.studentID
INNER JOIN dbo.IDuration id ON i.IepID = id.iepID
INNER JOIN AppointmentStudent as ON s.studentID = as.studentID
INNER JOIN Appointment a ON as.appointmentID = a.appointmentID
LEFT OUTER JOIN SchoolWeekYear swy on a.calWeekNumber = swy.calWeekNumber
INNER JOIN AppointmentTherapist at ON a.appointmentID = at.appointmentID
WHERE s.studentID = #studentID
GROUP BY col1, col2
) t
Is this possible?

Answer 1

You need to integrate SchoolWeekYear into the existing table set at an earlier stage.
To show you the principle, let us simplify the problem even further. Let there be a table called WeeklyData with columns WeekNumber and SomeData. Some weeks might have multiple entries, some others none. So this query
SELECT
WeekNumber,
AGG(SomeData)
FROM
WeeklyData
GROUP BY
WeekNumber
;
would return only weeks present in WeeklyData. If you want to return data for all weeks, use a corresponding reference table (let it be called AllWeeks) like this:
SELECT
aw.WeekNumber,
AGG(wd.SomeData)
FROM
AllWeeks AS aw
LEFT JOIN
WeeklyData AS wd ON aw.WeekNumber = wd.WeekNumber
GROUP BY
aw.WeekNumber
;
So, you take the reference table (AllWeeks) and join the data table (WeeklyData) to it, not the other round.
Now, what if the original query was slightly more complex? Let us now suppose the data table is called StudentWeeklyData and has a column called StudentID which is a reference to a Students table. Let us also imagine the query is similar to yours in that it logically includes the Students table before the data table is joined and filters the results on the primary key of Students:
SELECT
s.StudentID,
s.StudentName,
swd.WeekNumber,
AGG(swd.SomeData)
FROM
Students AS s
INNER JOIN
StudentWeeklyData AS swd ON s.StudentID = swd.StudentID
WHERE
s.StudentID = #StudentID
GROUP BY
s.StudentID,
s.StudentName,
swd.WeekNumber
;
(Not every detail matters here, I just wanted to use a more similar example for you that would still be simple enough to understand.) Again, this would return only weeks where the specified student has data in StudentWeeklyTable. If you wanted to return all weeks for the student (some of them potentially empty, of course), this is how you could go about it:
SELECT
s.StudentID,
s.StudentName,
aw.WeekNumber,
AGG(swd.SomeData)
FROM
Students AS s
CROSS JOIN
AllWeeks AS aw
LEFT JOIN
StudentWeeklyData AS swd ON s.StudentID = swd.StudentID
AND aw.WeekNumber = swd.WeekNumber
WHERE
s.StudentID = #StudentID
GROUP BY
s.StudentID,
s.StudentName,
aw.WeekNumber
;
Here you can see again that the AllWeeks table is included before the data table. The difference to the previous case is we are not left-joining the result of the join between Students and StudentWeekly to AllWeeks, nor are we left-joining the data table itself specifically to AllWeeks. Instead, the data table is joined to the result of a cross join, Students × AllWeeks.
Returning to your specific situation, I realise that in your case even more tables are involved. Since you are not specifying how all those tables are related to one another, I can only guess that SchoolWeekYear should be cross-joined somewhere after FROM and before this line:
INNER JOIN Appointment a ON as.appointmentID = a.appointmentID
and that the said line should be modified like this:
LEFT JOIN Appointment a ON as.appointmentID = a.appointmentID
AND swy.calWeekNumber = a.calWeekNumber
the swy being an alias assigned to SchoolWeekYear.
It is also worth noting that there is a subsequent inner join with AppointmentTherapist. That join would eliminate the effect of the above left join if it remained unchanged, because its condition references the Appointment table. Perhaps, the syntactically easiest way to fix the issue would be to change that inner join to a left one too, although there is another way: instead of
LEFT JOIN Appointment a ON as.appointmentID = a.appointmentID
AND swy.calWeekNumber = a.calWeekNumber
LEFT JOIN AppointmentTherapist at ON a.appointmentID = at.appointmentID
you could use this syntax:
LEFT JOIN
Appointment a
INNER JOIN AppointmentTherapist at ON a.appointmentID = at.appointmentID
ON as.appointmentID = a.appointmentID
AND swy.calWeekNumber = a.calWeekNumber
That way the logical order of joining would be changed: Appointment and AppointmentTherapist would be first inner-joined with each other, then the result set would be outer-joined to the result of the previously specified joins.

Answer 2

It is possible. But if you have multiple row with some calWeekNumber on the SchoolWeekYear table, your aggregate function return wrong result.

Answer 3

If you want all lines in SchoolWeekYear shown, regardless of a match, you should use RIGHT OUTER JOIN instead of LEFT.