xy720 commented on code in PR #64622:
URL: https://github.com/apache/doris/pull/64622#discussion_r3432249354
##########
fe/fe-core/src/main/java/org/apache/doris/nereids/trees/expressions/functions/SearchSignatureForRound.java:
##########
@@ -18,26 +18,84 @@
package org.apache.doris.nereids.trees.expressions.functions;
import org.apache.doris.catalog.FunctionSignature;
+import org.apache.doris.nereids.CascadesContext;
+import org.apache.doris.nereids.rules.expression.ExpressionRewriteContext;
+import org.apache.doris.nereids.rules.expression.rules.FoldConstantRuleOnFE;
+import org.apache.doris.nereids.trees.expressions.Cast;
import org.apache.doris.nereids.trees.expressions.Expression;
+import org.apache.doris.nereids.trees.expressions.literal.IntegerLikeLiteral;
import org.apache.doris.nereids.types.DoubleType;
import org.apache.doris.nereids.types.IntegerType;
+import org.apache.doris.nereids.types.coercion.Int32OrLessType;
+import java.util.ArrayList;
import java.util.List;
/**
- * if argument 0 is float or double, we should return double signature for
round like function.
+ * Signature search for round-like functions (round, round_bankers, ceil,
floor, truncate).
+ *
+ * For float/double inputs the result type defaults to double, which is
correct except
+ * when a non-negative integer-literal scale is given: the rounded double
cannot land on a
+ * clean N-decimal value (e.g. round(23900/293, 2) stores 81.56999999999999488…
+ * in IEEE-754 and renders as "81.56999999999999").
+ * In that case, for DOUBLE input we route the call through the existing
decimal
+ * signature, which both gives the user the value they asked for and matches
MySQL's
+ * behavior. FLOAT input is left on the original DOUBLE path: float promotes to
+ * decimal(14, 7) which can only hold 7 integer digits —- values |f| >= 1e7
would
+ * overflow during the cast.
*/
public interface SearchSignatureForRound extends ExplicitlyCastableSignature {
+
+ int DOUBLE_DECIMAL_RESULT_MAX_SCALE = 15;
+
@Override
default FunctionSignature searchSignature(List<FunctionSignature>
signatures) {
List<Expression> arguments = getArguments();
if (arguments.get(0).getDataType().isFloatLikeType()) {
if (arguments.size() == 1) {
return
FunctionSignature.ret(DoubleType.INSTANCE).args(DoubleType.INSTANCE);
} else if (arguments.size() == 2) {
+ if (arguments.get(0).getDataType().isDoubleType()
+ && isNonNegativeIntegerLiteralAtMost(arguments.get(1),
+ DOUBLE_DECIMAL_RESULT_MAX_SCALE)) {
Review Comment:
Add a session variables round_double_returns_decimal_for_const_scale,
default is set to false.
This fix will take effect only `set
round_double_returns_decimal_for_const_scale = true`
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