sql: add unimplemented error for recursive query without union all

[awoods187]

Consider this table:

CREATE TABLE edges (
   src integer,
   dest integer
);

INSERT INTO edges (
    src,
    dest
)
VALUES
    (1, 2),
    (2, 3),
    (2, 4),
    (3, 4),
    (4, 1),
    (3, 5);

And this query:

WITH RECURSIVE paths (src, dest, path) AS (
        SELECT e.src, e.dest, ARRAY[e.src, e.dest]
        FROM edges e
    UNION
        SELECT p.src, e.dest, p.path || ARRAY[e.dest]
        FROM paths p
        JOIN edges e
        ON p.dest = e.src AND e.dest != ALL(p.path)
)
SELECT * FROM paths;

Returns:

ERROR: recursive query "paths" does not have the form non-recursive-term UNION ALL recursive-term
SQLSTATE: 42601

We should update this to include the unimplemeted error and github issue.

[RaduBerinde]

Is there an issue for recursive CTEs with UNION? I seem to recall you filed one but I can't find it.