tree 747fa234bd14c3b7d4d23065a41d0c767c7e493b
parent 96cbd709caff1084ca190ec45c76f2092c33a52b
author Julian Hyde <jhyde@apache.org> 1628051780 -0700
committer Julian Hyde <jhyde@apache.org> 1628286223 -0700

[CALCITE-4485] JDBC adapter generates invalid SQL when one of the joins is "INNER JOIN ... ON TRUE"

If the join tree is a mixture of cross-joins and outer joins,
RelToSqlConverter wrongly generates comma-join syntax.
Consider the (pseudo) RelNode tree

    CrossJoin(a, LeftJoin(b, CrossJoin(c, d)))

Before this bug was fixed, RelToSqlConvert would generate

    FROM a, b LEFT JOIN c, d

Because LEFT JOIN has higher precedence than ',', this is parsed to

    LeftJoin(CrossJoin(a, b), CrossJoin(c, d))

which is incorrect. The fix is to only generate comma-join syntax
if all joins are cross-joins. In this case, we will generate
(pseudo SQL)

  FROM a CROSS JOIN b LEFT JOIN c CROSS JOIN d

which is safe.