[jira] [Created] (CALCITE-4485) Invalid SQL being produced by RelToSqlConverter when the join condition is tautology

["Ondřej Štumpf (Jira)" <ji...@apache.org>]

Ondřej Štumpf created CALCITE-4485:
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             Summary: Invalid SQL being produced by RelToSqlConverter when the join condition is tautology
                 Key: CALCITE-4485
                 URL: https://issues.apache.org/jira/browse/CALCITE-4485
             Project: Calcite
          Issue Type: Bug
          Components: core
            Reporter: Ondřej Štumpf


h5. Summary
When using {{INNER}} join and a join condition that is always true, the {{RelToSqlConverter}} may generate invalid an SQL.

h5. Reproducer (Kotlin; TPCH dataset)
{code:java}
val frameworkConfig = ...
val relationalBuilder = RelBuilder.create(frameworkConfig)

val rootRelationalNode = relationalBuilder
    .scan("tpch", "customer")
    .aggregate(
        relationalBuilder.groupKey(
            relationalBuilder.field("nation_name")
        ),
        relationalBuilder.count().`as`("cnt1")
    )
    .project(relationalBuilder.field("nation_name"), relationalBuilder.field("cnt1"))
    .`as`("cust")
    .scan("tpch", "lineitem")
    .aggregate(
        relationalBuilder.groupKey(),
        relationalBuilder.count().`as`("cnt2")
    )
    .project(relationalBuilder.field("cnt2"))
    .`as`("lineitem")
    .join(JoinRelType.INNER)
    .scan("tpch", "part")
    .join(
        JoinRelType.LEFT,
        relationalBuilder.call(
            SqlStdOperatorTable.EQUALS,
            relationalBuilder.field(2, "cust", "nation_name"),
            relationalBuilder.field(2, "part", "p_brand")
        )
    )
    .project(
        relationalBuilder.field("cust", "nation_name"),
        relationalBuilder.alias(
            relationalBuilder.call(
                SqlStdOperatorTable.MINUS,
                relationalBuilder.field("cnt1"),
                relationalBuilder.field("cnt2")
            ),
            "f1")
    )
    .build()

println(
    RelToSqlConverter(SqlDialect.DatabaseProduct.POSTGRESQL.dialect)
        .visitRoot(rootRelationalNode)
        .asStatement()
        .toSqlString(SqlDialect.DatabaseProduct.POSTGRESQL.dialect)
        .sql
)
{code}

h5. Result SQL
{code:sql}
SELECT "t"."c_name", "t"."cnt1" - "t0"."cnt2" AS "f1"
FROM (SELECT "c_name", COUNT(*) AS "cnt1"
      FROM "tpch"."customer"
      GROUP BY "c_name") AS "t",
     (SELECT COUNT(*) AS "cnt2"
      FROM "tpch"."lineitem") AS "t0"
         LEFT JOIN "tpch"."part" ON "t"."c_name" = "part"."p_brand"
{code}
which produces error (on Postgres):
{code}
[42P01] ERROR: invalid reference to FROM-clause entry for table "t" Hint: There is an entry for table "t", but it cannot be referenced from this part of the query. Position: 265
{code}

h5. Expected SQL
{code:sql}
SELECT "t"."c_name", "t"."cnt1" - "t0"."cnt2" AS "f1"
FROM (SELECT "c_name", COUNT(*) AS "cnt1"
      FROM "tpch"."customer"
      GROUP BY "c_name") AS "t" CROSS JOIN
     (SELECT COUNT(*) AS "cnt2"
      FROM "tpch"."lineitem") AS "t0"
         LEFT JOIN "tpch"."part" ON "t"."c_name" = "part"."p_brand"
{code}

h5. Suggestion for a fix
The {{CROSS JOIN}} syntax was introduced in SQL 92 and seems to be widely supported by DB engines, therefore I suggest to change the default in {{SqlDialect#emulateJoinTypeForCrossJoin}} from {{JoinType.COMMA}} to {{JoinType.CROSS}}.
I have checked all supported DB products from {{SqlDialect.DatabaseProduct}} and they all seem to support the {{CROSS JOIN}} syntax, except these, which I have not been able to verify: Infobright, Luciddb, Paraccel, Netezza. For sake of backward compatibility, I suggest to override the {{emulateJoinTypeForCrossJoin}} method in these dialects to behave as before, i.e. {{JoinType.COMMA}}.




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