georgia-tech-db/spes

Tool for checking whether two SQL queries are equivalent

spes's Issues

Potential unsoundness when translating outer joins

The following logic in JoinParser.java translates an outer join with join condition that is trivially true into an inner join with the same condition.

spes/src/main/java/AlgeNodeParser/JoinParser.java

Lines 44 to 49 in 8049f98

	if (joinCondition.getKind() == SqlKind.LITERAL) {
	RexLiteral maybeTrue = (RexLiteral) joinCondition;
	if (maybeTrue.isAlwaysTrue()){
	return constructNode(result,z3Context);
	}
	}

However, a left outer join with join condition TRUE would still generate null rows when the right table is empty, making it nonequivalent to an inner join.

The branch right above also seems off.

spes/src/main/java/AlgeNodeParser/JoinParser.java

Lines 41 to 43 in 8049f98

	if (joinCondition.getKind() == SqlKind.IS_TRUE) {
	return constructNode(result,z3Context);
	}

I believe SqlKind.IS_TRUE indicates the IS TRUE operator, not that the condition is trivially true. Translating R1 LEFT JOIN R2 ON P IS TRUE into R1 INNER JOIN R2 ON P IS TRUE for arbitrary predicate P is clearly not right.

Please let me know if I am misunderstanding anything. Thank you!