-- jsonb_to_recordset reads every column it declares for the elements of the documents that reach it, also the ones the query does not read. The scan
-- reads again the rows whose document holds a value such a column refuses (a string where it is a float8); when a conjunct of the rows reads the same list
-- it cannot, as the error would come before the conjunct drops the row, so the query keeps its plan instead of failing with the scan's own error for a
-- document PostgreSQL never gives to the function. Only whether the results agree is printed.
CREATE EXTENSION pg_sift;
SET max_parallel_workers_per_gather = 0;
SET sift.agg_preagg = off;
CREATE TABLE docs (id int, doc jsonb);
INSERT INTO docs
SELECT i, jsonb_build_object('items', jsonb_build_array(jsonb_build_object('category', CASE WHEN i = 777 THEN 'z' ELSE 'a' || i % 3 END,
                                                                            'score', CASE WHEN i = 777 THEN '"abc"'::jsonb ELSE to_jsonb(i % 5) END),
                                                        jsonb_build_object('category', 'b', 'score', 2)))
FROM generate_series(1, 5000) i;
CREATE INDEX docs_col ON docs USING sift_col (id, doc) WITH (paths = 'doc.items[]{category text, score float8}');
VACUUM (FREEZE, ANALYZE) docs;
\ir test/agg_helpers.sql
CREATE FUNCTION same(q text) RETURNS bool LANGUAGE sql AS $$ SELECT outcome(q, false) = outcome(q, true) $$;
-- the element 'z' fails the EXISTS, so its score is never read
SELECT same($q$
 SELECT e.category, count(*) AS n FROM docs d CROSS JOIN LATERAL jsonb_to_recordset(d.doc->'items') e(category text, score float8)
 WHERE EXISTS (SELECT 1 FROM jsonb_to_recordset(d.doc->'items') x(category text) WHERE x.category = 'a1') GROUP BY 1
$q$) AS exists_drops_row;
-- the same without the conjunct: the document reaches the function, and both plans raise its error
SELECT same($q$
 SELECT e.category, count(*) AS n FROM docs d CROSS JOIN LATERAL jsonb_to_recordset(d.doc->'items') e(category text, score float8) GROUP BY 1
$q$) AS row_reaches_function;
SELECT outcome($q$
 SELECT e.category, count(*) AS n FROM docs d CROSS JOIN LATERAL jsonb_to_recordset(d.doc->'items') e(category text, score float8) GROUP BY 1
$q$, true) AS error;
DROP FUNCTION same(text), outcome(text, bool), runs_in_scan(text), pushed, runq;
DROP TABLE docs;
DROP EXTENSION pg_sift;