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Classic ASP Databases Discuss using ASP 3 to work with data in databases, including ASP Database Setup issues from the old P2P forum on this specific subtopic. See also the book forum Beginning ASP.NET Databases for questions specific to that book. NOT for ASP.NET 1.0, 1.1, or 2.0.
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Old August 23rd, 2006, 10:28 AM
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Default Joining Three Tables

Hello all

From having an ID number of a field in a favs table, which is the same as that in the books table, I need to retrieve information about the book. I can get this to work but I also need to join to a third table, the user table by using the userID in the books table and joining to the user table to then retrieve informaiton about that user.

I hope this makes sense.
The code I have written is below, it should be evident from this what I want to do.

strSQL = "SELECT favs.ID, favs.objectID, favs.object_type, books.ID, books.userID, books.title, books.author, restrictedAccess_db.first_name, restrictedAccess_db.surname, restrictedAccess_db.email "
strSQL = strSQL & "FROM favs "
strSQL = strSQL & "LEFT JOIN books "
strSQL = strSQL & "ON favs.objectID = books.ID "
strSQL = strSQL & "JOIN restrictedAccess_db "
strSQL = strSQL & "ON books.userID = restrictedAccess_db.userID "
strSQL = strSQL & "WHERE favs.objectID = '" & u_ID & "' And favs.object_type = 'book' "
strSQL = strSQL & "ORDER BY books.title;"

This gives me the following error:

Syntax error (missing operator) in query expression 'favs.objectID = books.ID JOIN restrictedAccess_db ON books.userID = restrictedAccess_db.userID'.


I hope someone can help.

Thanks in advance.

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Old August 23rd, 2006, 12:29 PM
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Default

Hmm that should be fine...I wrote this in query analyzer and it parsed ok

SELECT
    f.id,
    f.objectID,
    f.object_type,
    b.id,
    b.userID,
    b.title,
    b.author,
    r.firstName,
    r.surName,
    r.email
FROM
    favs f
LEFT JOIN
    Books b
ON
   f.objectID = b.ID
LEFT JOIN
   restrictedAccess_db r
ON
   b.UserID = r.UserID
WHERE
   f.objectID =@value AND f.object_type = 'book'
ORDER BY
   b.title

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Old August 31st, 2006, 04:13 PM
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Perhaps this line:
Code:
strSQL = strSQL    & "JOIN restrictedAccess_db "
should be changed to this:
Code:
strSQL = strSQL    & "INNER JOIN restrictedAccess_db "
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Old September 1st, 2006, 07:40 AM
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The type of join they use is relative to the data they are trying to retrive; I favor Outer Joins (in my example a Left Join) so that I can deal with any data that may be NULL.

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Old September 1st, 2006, 03:50 PM
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Perhaps... and in this case, it is unclear that using a second outer join makes any sense, let alone the first one. Why bother bringing data back at all for the "favs" of a user who doesn't exist? Then you don't have to deal with the NULLS or anything else for that matter.

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Old September 1st, 2006, 04:08 PM
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Again it is all strictly relative to what you are trying to do; there are instances where you need to do with NULL values, however, it is pointless to debate on this as we haven't a clue what the database looks like, values that should be returned, yadda yadda yadda. Good insight though woody.

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