通过ODBC使用MS Access 2003进行嵌套的内部联接

Question

If this works:

SELECT COUNT(t1.ID) AS count FROM Project t1
INNER JOIN (SELECT DISTINCT t.Site,t.id FROM _Equipment_id t WHERE t.OEM LIKE '%ABC%') t2 ON t1.Site=t2.Site AND t1.id=t2.id

and this works:

SELECT COUNT(t3.ID) AS count FROM Wall t3
INNER JOIN Project t1 ON t3.Project_number=t1.Project_number

Why doesn't this work:

SELECT COUNT(t3.ID) AS count FROM Wall t3
INNER JOIN Project t1 ON t3.Project_number=t1.Project_number
INNER JOIN (SELECT DISTINCT t.Site,t.id FROM _Equipment_id t WHERE t.OEM LIKE '%ABC%') t2 ON t1.Site=t2.Site AND t1.id=t2.id

Ultimately, I have 10 tables like the Wall table that I am trying to get a total count from the first SELECT....

Answer 1

SELECT COUNT(t3.ID) AS count FROM Wall t3
INNER JOIN (Project t1 
INNER JOIN (SELECT DISTINCT t.Site,t.id FROM _Equipment_id t WHERE t.OEM LIKE '%ABC%') t2 
ON t1.Site=t2.Site AND t1.id=t2.id)
ON t3.Project_number=t1.Project_number

Maybe it's just a syntax error? Office Help at the bottom where they mention nesting. The other possibility is that the aliases are somehow scoped so that they are not available to the join, but I'm no expert on MS Access. Maybe you should just try dropping the aliases altogether.

Answer 2

You have a couple of minor issues with your code: a table name that starts with an underscore character ( _Equipment_id ) and an AS clause ("alias") that is a SQL keyword ( AS count ). When these are corrected, your SQL is valid SQL-92 syntax.

Sadly, the problem is that Access (ACE, Jet, whatever) does not support the SQL-92 Standard. Access insists that each nested JOIN clause is put in parentheses.

[Aside: JOIN s in parentheses are allowed in Standard SQL because it can potentially change the query results. However Access, does not respect the order specified by the coder and allows itself to evaluate JOIN s in order it sees fir. So not only Access's syntax non-compliant with the Standard, there is also a loss of functionality! However, this further problem with Access will have no ill effect for this particular query.]

You have two JOIN s in the same scope here:

...
INNER JOIN Project t1 ON t3.Project_number=t1.Project_number
INNER JOIN
...

Your code needs to work around Access's problem by enclosing the JOIN in parentheses; because all your JOIN s are INNER flavour, it probably doesn't matter where they go.

Also, as regards correcting your AS clause, Access again doesn't support Standard SQL's quoted identifiers ( ...AS "count"... ) and insists you use its proprietary square brackets syntax ( ...AS [count]... ) -- of course, you could choose a different name but there may exist application code that relies on it.

Code to workaround both Access problems:

SELECT COUNT(t3.ID) AS [count] 
  FROM (Wall t3
       INNER JOIN Project AS t1 
          ON t3.Project_number = t1.Project_number)
       INNER JOIN (
                   SELECT DISTINCT t.Site,t.id 
                     FROM _Equipment_id AS t 
                    WHERE t.OEM LIKE '%ABC%'
                  ) AS t2 
          ON t1.Site = t2.Site 
             AND t1.id = t2.id;