Left Join Yielding no results

[Sconibulus]

I'm coming across an issue where when I write a query as so:

SELECT a.v, b.w, c.x, d.y, e.z
FROM a
JOIN b
on a.id = b.id
LEFT JOIN c
on a.id = c.id
LEFT JOIN d
on b.code=d.code
JOIN e
on a.n = e.n
WHERE
a.zone = 10
WITH (nolock)


I get several hundred results, but when I modify it to this:

SELECT a.v, b.w, c.x, d.y, e.z
FROM a
JOIN b
on a.id = b.id
LEFT JOIN c
on a.id = c.id AND c.n = 0
LEFT JOIN d
on b.code=d.code AND d.n = 0
JOIN e
on a.n = e.n
WHERE
a.zone = 10
WITH (nolock)


I get zero results.

From my understanding of SQL and left joins, I feel that getting any results with the first query means I should definitely get at least one result with the second, if only one where fields from c and d are null. Does PROGRESS implement outer joins in an unusual manner?

Continue reading...