CODEWITHSUNDEEP
sqlsql-server-2008join
user2680645
user2680645

Reputation: 1

Too many results - SQL join issues

I've never posted here, so hoping this goes well :). I am using SQL Server 2008 R2 and I am trying to extract Student/Course information from a database. Here is what I am dealing with:

Table dbo.StudentsSchedule

StudentsSchedule table contains the following fields: CRS_CODE CRS_SECT ID_NUMBER

Table dbo.StaffSchedule:

COURSE SECTION Teacher_ID

Here is what I am trying to accomplish:

I would like to combine the COURSE+SECTION CODE+Teacher_ID to use that as a Unique "New Course ID" and then attach a Student to it.

I've attempted this but I am getting way too many results. I am expecting around 300 but receiving over 10K+

 SELECT dbo.StaffSchedule.COURSE+'-'+ dbo.StaffSchedule.SECTION+'-'+dbo.StaffSchedule.Teacher_ID) as [NewCourseID],
          dbo.StudentSchedule.ID_NUMBER AS [StudentID],
          from dbo.StaffSchedule INNER JOIN dbo.StudentSchedule ON
   dbo.StaffSchedule.COURSE=dbo.StudentSchedule.CRS_CODE and
   dbo.StaffSchedule.SECTION=dbo.StudentSchedule.CRS_SECT

Note that Teacher_ID can only exist once per COURSE+SECTION.

Any ideas? Am I doing this wrong?

Upvotes: 0

Views: 187

Answers (1)

GianlucaBobbio
GianlucaBobbio

Reputation: 184

Lets try to see it

Table dbo.StaffSchedule:

COURSE SECTION Teacher_ID

  1       1      23
  1       1      24
  1       3      55
  1       3      24

Table dbo.StudentsSchedule:

CRS_CODE CRS_SECT ID_NUMBER

   1        1       44
   1        1       45
   1        3       89
   1        3       44

This code:

   SELECT dbo.StaffSchedule.COURSE+'-'+ dbo.StaffSchedule.SECTION+'-'+dbo.StaffSchedule.Teacher_ID) as [NewCourseID], dbo.StudentSchedule.ID_NUMBER AS [StudentID]
   from dbo.StaffSchedule INNER JOIN dbo.StudentSchedule ON
   dbo.StaffSchedule.COURSE=dbo.StudentSchedule.CRS_CODE and
   dbo.StaffSchedule.SECTION=dbo.StudentSchedule.CRS_SECT

will return:

NewCourseID StudentID

   1-1-23        44
   1-1-23        45
   1-1-24        44
   1-1-24        45
   1-3-55        89
   1-3-24        89
   1-3-55        44
   1-3-24        44

May be the only problem I see is that for the same StudentID you have more than one value. I don't know what are you specting, so this is hoy much I can help you.

Sorry for my bad english! I hope this can help!

EDITE FOR NEW COMMENT

Is really simple to not use de Section in the NewCourseId

   SELECT dbo.StaffSchedule.COURSE+'-'+dbo.StaffSchedule.Teacher_ID) as [NewCourseID],   dbo.StudentSchedule.ID_NUMBER AS [StudentID]
   from dbo.StaffSchedule INNER JOIN dbo.StudentSchedule ON
   dbo.StaffSchedule.COURSE=dbo.StudentSchedule.CRS_CODE and
   dbo.StaffSchedule.SECTION=dbo.StudentSchedule.CRS_SECT

But... what will happen? The result will be:

NewCourseID StudentID

   1-23        44
   1-23        45
   1-24        44
   1-24        45
   1-55        89
   1-24        89
   1-55        44
   1-24        44

Look what happened whit the ID 1-24, it's look to has duplicated values, do you understand why? Look at the original tables again.

Sorry for my bad english!

Upvotes: 1

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