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I have two tables: (condensed version of Subject) Subject and MessageSubject
CREATE TABLE [dbo].[Subject](
[SubjectID] [int] IDENTITY(1,1) NOT NULL,
[Name] [nchar](80) NULL,
[Active] [bit] NULL
) ON [PRIMARY]
CREATE TABLE [dbo].[MessageSubject](
[MessageSubjectID] [int] IDENTITY(1,1) NOT NULL,
[MessageID] [int] NOT NULL,
[SubjectID] [int] NOT NULL
) ON [PRIMARY]
Not shown is the table 'Message' but every message has one or more subjects (MessageSubject entries)
What I need to do is find all the subjects that were posted to a message 'with' a a given subject, not including the given SubjectID.
My guess is a #temp table or CTE or something is the way to do it, but I can't seem to find out how to do in SQL:
The procedure below is the format I need it to be (if possible) but here is what I am doing in C# code now:
I currently find all the messages for a given subject:
Then I have to query all the MessageSubject (subjects) for each message;
IF any subjects were found for a message other than the source SubjectID (related subjects) I check my list of subjects and if the index of the new related subject is not found I add it to the list.
This means I am performing ('x' + 1) number of queries for each Subject where 'x' = the number of messages and 1 query to find all the messages for the subject.
I know there has to be a way to find to find the 'Related Subject', but I can't seem to get my head around it.
Any help is appreciated, thanks.
Create PROCEDURE [dbo].[Subject_FindRelatedSubjects]
-- SubjectID Parametere
@SubjectID int
AS
BEGIN
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON
-- Begin Select Statement
Select [Active],[Name],[SubjectID]
-- From tableName
From [Subject] s Inner Join [MessageSubject] ms on s.SubjectID = ms.SubjectID
-- Find Subjects That Were Posted 'With' the SubjectID given
Where ...
END

Answer 1

Create PROCEDURE [dbo].[Subject_FindRelatedSubjects]
    -- SubjectID Parametere
    @SubjectID int
AS
BEGIN
    -- SET NOCOUNT ON added to prevent extra result sets from
    -- interfering with SELECT statements.
    SET NOCOUNT ON
    -- CTE For All Messages For This SubjectID
    ;WITH cteMessages AS
        -- Select All MessageIDs for the given SubjectID
 Select MessageID From MessageSubject ms Where ms.SubjectID = @SubjectID
    ), cteMessageSubjects As
        -- Select Only The SubjectID From CTE Messages
        Select SubjectID From MessageSubject ms2
        -- Only return iems from MessageSubject table where the SubjecteID is not equal to  @SubjectID Where ms2.SubjectID != @SubjectID
        -- And The MessageID In cteMessages
        And ms2.MessageID In (Select MessageID From cteMessages)
 -- Select Fields
 Select [Active],[Name][SubjectID]
 -- From Table Name
 From Subject
 -- Only Return Subjects In cteSubjects
 Where SubjectID in (Select SubjectID From cteSubjects)
END