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[CALCITE-6027] Simplify the cardinality on map_keys and map_values functions #5037

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[CALCITE-6027] Simplify the cardinality on map_keys and map_values functions #5037

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16 changes: 16 additions & 0 deletions core/src/main/java/org/apache/calcite/rex/RexSimplify.java
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Original file line number Diff line number Diff line change
Expand Up @@ -408,6 +408,22 @@ RexNode isFalse(RexNode e) {
private RexNode simplifyGenericNode(RexCall e) {
final List<RexNode> operands = new ArrayList<>(e.operands);
simplifyList(operands, UNKNOWN);

// Simplify CARDINALITY(MAP_KEYS(m)) -> CARDINALITY(m)
// and CARDINALITY(MAP_VALUES(m)) -> CARDINALITY(m)
if (e.getOperator().getName().equals("CARDINALITY")

@mihaibudiu mihaibudiu Jun 22, 2026

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Do you expect people write such programs?
There's potentially an infinite number of such optimizations we can consider, but are they useful in practice?

@xuzifu666 xuzifu666 Jun 23, 2026

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You are right. This is indeed an overly restrictive optimization, with little value; I currently share this view. Perhaps the value of Jira needs further discussion.

@xuzifu666 xuzifu666 Jun 23, 2026

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I had moved the discussion to jira.

&& operands.size() == 1
&& operands.get(0) instanceof RexCall) {
final RexCall innerCall = (RexCall) operands.get(0);
final SqlKind innerKind = innerCall.getKind();
if (innerKind == SqlKind.MAP_KEYS || innerKind == SqlKind.MAP_VALUES) {
// CARDINALITY(MAP_KEYS(m)) -> CARDINALITY(m)
// CARDINALITY(MAP_VALUES(m)) -> CARDINALITY(m)
final RexNode map = innerCall.getOperands().get(0);
return rexBuilder.makeCall(e.getParserPosition(), e.getOperator(), map);
}
}

if (e.operands.equals(operands)) {
return e;
}
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60 changes: 60 additions & 0 deletions core/src/test/java/org/apache/calcite/rex/RexBuilderTest.java
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Expand Up @@ -1524,4 +1524,64 @@ private static class UDT extends RelDataTypeImpl {
literal, literal, flag),
notNullValue());
}

@Test void testCardinalityMapKeysSimplification() {
final RexImplicationCheckerFixtures.Fixture f =
new RexImplicationCheckerFixtures.Fixture();
final RexBuilder rexBuilder = f.rexBuilder;

// Create map literal: map['foo', 1, 'bar', 2]
final RexLiteral fooKey = rexBuilder.makeLiteral("foo");
final RexLiteral oneVal = rexBuilder.makeExactLiteral(new java.math.BigDecimal(1));
final RexLiteral barKey = rexBuilder.makeLiteral("bar");
final RexLiteral twoVal = rexBuilder.makeExactLiteral(new java.math.BigDecimal(2));
final RexNode mapLiteral =
rexBuilder.makeCall(SqlStdOperatorTable.MAP_VALUE_CONSTRUCTOR,
fooKey, oneVal, barKey, twoVal);

// Create CARDINALITY(MAP_KEYS(map))
final RexNode mapKeys =
rexBuilder.makeCall(SqlLibraryOperators.MAP_KEYS, mapLiteral);
final RexNode cardinalityMapKeys =
rexBuilder.makeCall(SqlStdOperatorTable.CARDINALITY, mapKeys);

// Simplify
final RexNode simplified = f.simplify.simplify(cardinalityMapKeys);

// Expected: CARDINALITY(map)
final RexNode expectedCardinalityMap =
rexBuilder.makeCall(SqlStdOperatorTable.CARDINALITY, mapLiteral);

assertThat(simplified, hasToString(expectedCardinalityMap.toString()));
}

@Test void testCardinalityMapValuesSimplification() {
final RexImplicationCheckerFixtures.Fixture f =
new RexImplicationCheckerFixtures.Fixture();
final RexBuilder rexBuilder = f.rexBuilder;

// Create map literal: map['foo', 1, 'bar', 2]
final RexLiteral fooKey = rexBuilder.makeLiteral("foo");
final RexLiteral oneVal = rexBuilder.makeExactLiteral(new java.math.BigDecimal(1));
final RexLiteral barKey = rexBuilder.makeLiteral("bar");
final RexLiteral twoVal = rexBuilder.makeExactLiteral(new java.math.BigDecimal(2));
final RexNode mapLiteral =
rexBuilder.makeCall(SqlStdOperatorTable.MAP_VALUE_CONSTRUCTOR,
fooKey, oneVal, barKey, twoVal);

// Create CARDINALITY(MAP_VALUES(map))
final RexNode mapValues =
rexBuilder.makeCall(SqlLibraryOperators.MAP_VALUES, mapLiteral);
final RexNode cardinalityMapValues =
rexBuilder.makeCall(SqlStdOperatorTable.CARDINALITY, mapValues);

// Simplify
final RexNode simplified = f.simplify.simplify(cardinalityMapValues);

// Expected: CARDINALITY(map)
final RexNode expectedCardinalityMap =
rexBuilder.makeCall(SqlStdOperatorTable.CARDINALITY, mapLiteral);

assertThat(simplified, hasToString(expectedCardinalityMap.toString()));
}
}
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