The following bug has been logged on the website:
Bug reference: 15741
Logged by: Anthony SKORSKI
Email address: skorski.anthony@gmail.com
PostgreSQL version: 10.6
Operating system: Ubuntu 18.04
Description:
Hi
Trying to build a tool which automatically builds queries to "flatten" JSONB
fields, I came to a `ERROR: failed to build any 3-way joins` message while
trying to execute some of those queries.
It is reproducible from a simple table...
`CREATE TABLE random_table (random_field JSONB);`
... some JSON data in nested arrays ...
`INSERT INTO public.random_table (random_field) VALUES ('{"bar": [[[1, 2, 3,
4]]], "foo": [[["abc", "def"], ["tuw", "xyz"]]]}');`
... and a WIP query to flatten this JSON data.
```
SELECT *
FROM random_table
LEFT OUTER JOIN LATERAL (
SELECT *
FROM jsonb_array_elements(random_table.random_field -> 'foo')
WITH ORDINALITY AS foo_level_1(foo_1, foo_1_index)
LEFT OUTER JOIN LATERAL (
SELECT *
FROM jsonb_array_elements(foo_1)
WITH ORDINALITY AS foo_level_2(foo_2, foo_2_index)
--LEFT OUTER JOIN LATERAL (
-- SELECT *
-- FROM jsonb_array_elements(foo_2)
-- WITH ORDINALITY AS foo_level_3(foo_3, foo_3_index)
--) AS foo_lateral_2 ON TRUE
) AS foo_lateral_1 ON TRUE
FULL OUTER JOIN jsonb_array_elements(random_table.random_field ->
'bar')
WITH ORDINALITY AS bar_level_1(bar_1, bar_1_index) ON FALSE
LEFT OUTER JOIN LATERAL (
SELECT *
FROM jsonb_array_elements(bar_1)
WITH ORDINALITY AS bar_level_2(bar_2, bar_2_index)
) AS bar_lateral_1 ON TRUE
) AS pouet ON TRUE;
```
Note the commented part. As is the query works as expected (for its WIP
sstatus).
Once uncommented, the `ERROR: failed to build any 3-way joins` occurs and I
did not find anything about such a potential Postgresql limitation or any
workaround.
This behavior occurs on every Postgres version I tested. A fiddle is
available here to highlight the problem:
https://dbfiddle.uk/?rdbms=postgres_10&fiddle=0c40ba750b3e477e002f879edd0d6841
Please let me know if it actually is a bug and if it has a chance to be
fixed.
Regards.
