The first recursive view definition demonstrates a correct use of a left outer join, which is bold. The usage is valid because the recursive relation in the recursive statement of the view definition is used as the outer relation in the left outer join.
CREATE RECURSIVE VIEW rec (f1, mycount) AS (
SELECT a1, 0 AS mycount
FROM nonrec
UNION ALL
SELECT a2, mycount + 1
FROM rec LEFT OUTER JOIN nonrec ON nonrec.a1 = rec.f1
WHERE rec.mycount <= 100);
The second recursive view definition demonstrates a non-valid use of a left outer join, which is bold. The usage is not valid because the recursive relation in the recursive statement of the view definition is used as the inner relation in the left outer join.
CREATE RECURSIVE VIEW rec (f1, mycount) AS (
SELECT a1, 0 AS mycount
FROM nonrec
UNION ALL
SELECT a2, mycount + 1
FROM nonrec LEFT OUTER JOIN rec ON nonrec.a1 = rec.f1
WHERE rec.mycount <= 100);
You can use left outer joins without restriction in the seed statement of a recursive view definition.