UNION / EXCEPT / INTERSECT miss shared rows when the first SELECT has its own ORDER BY #2612

A set operation whose first SELECT has its own ORDER BY gives a wrong result for UNION, EXCEPT and INTERSECT when both SELECTs share a row. No error is raised. UNION ALL is not affected.

Reproduced on develop (v4.20.1), with the statement cache off:

alasql.options.cache = false;
alasql('CREATE TABLE e1 (a INT); INSERT INTO e1 VALUES (1),(2),(3),(4)');
alasql('CREATE TABLE e2 (a INT); INSERT INTO e2 VALUES (1),(5)');

Cause

queryfn3 in src/38query.js (the early ORDER BY / LIMIT step added in #2417). To sort the first SELECT before the set operation, it writes the order keys ($$$0, $$$1, ...) onto the first SELECT's rows. They are only removed by removeKeys at the end of queryfn3, after the set operation.

arrayUnionDeep, arrayExceptDeep and arrayIntersectDeep compare whole rows, so a row from the first SELECT ({a: 1, $$$0: 1}) never equals the same row from the second SELECT ({a: 1}).

Direction

Remove the order keys from the first SELECT's rows right after the early sort, before the set operation runs.

Tests: the queries in the table above, run twice each (see #2605).

Related: #2414, #2417, #2605 / #2608 (found while reviewing it), #2582 (rewrites the same block in queryfn3).