Jasmin Trada created CALCITE-7811:
-------------------------------------
Summary: RexImplicationChecker incorrectly proves NOT(x = a)
implies (x = a OR x = b)
Key: CALCITE-7811
URL: https://issues.apache.org/jira/browse/CALCITE-7811
Project: Calcite
Issue Type: Bug
Reporter: Jasmin Trada
RexImplicationChecker.implies() can return true for an implication that does not
actually hold, when the premise contains NOT wrapped directly around a
comparison
(e.g. NOT(x = a)).
Repro:
{code:java}
final Fixture f = new Fixture();
final RexNode sEqA = f.eq(f.str, f.charLiteral("a"));
final RexNode sEqB = f.eq(f.str, f.charLiteral("b"));
final RexNode sNeA = f.ne(f.str, f.charLiteral("a"));
final RexNode sNotEqA = f.rexBuilder.makeCall(SqlStdOperatorTable.NOT, sEqA);
final RexNode sEqAOrEqB = f.or(sEqA, sEqB);
// Correct: the checker soundly declines to prove this (x = 'c' is a
counterexample).
assertFalse(f.checker.implies(sNeA, sEqAOrEqB));
// Bug: the logically identical NOT(x = 'a') is wrongly reported as implying
the OR.
assertTrue(f.checker.implies(sNotEqA, sEqAOrEqB)); // should be false
{code}
"x <> 'a'" and "NOT(x = 'a')" are logically identical, but the checker treats
them
differently: only the syntactic NOT_EQUALS form is handled soundly. NOT(x = 'a')
is silently misrecorded internally as a plain x = 'a' usage, so the checker
"proves"
NOT(x = 'a') implies (x = 'a' OR x = 'b') by testing x = 'a' against the
right-hand
side, instead of testing x <> 'a'.
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