nandorKollar commented on code in PR #12969:
URL: https://github.com/apache/iceberg/pull/12969#discussion_r2101928619
##########
api/src/main/java/org/apache/iceberg/transforms/Truncate.java:
##########
@@ -513,5 +516,35 @@ public UnboundPredicate<BigDecimal> projectStrict(
}
return null;
}
+
+ @Override
+ public Type getResultType(Type sourceType) {
+ if (sourceType.typeId() != Type.TypeID.DECIMAL) {
+ // This should ideally not happen if canTransform and bind are used
correctly,
+ // but it's good practice to validate the input type.
+ throw new IllegalArgumentException(
+ "Truncate transform requires a DECIMAL type, but got: " +
sourceType);
+ }
+
+ Types.DecimalType decimal = (Types.DecimalType) sourceType;
+ int precision = decimal.precision();
+ int scale = decimal.scale();
+
+ // Convert truncate width into BigDecimal: w * 10^(-scale)
+ BigDecimal unit = new BigDecimal(unscaledWidth, scale);
+
+ // Determine input bound
+ BigDecimal minInput =
+ BigDecimal.TEN
+ .pow(precision - scale)
+ .subtract(BigDecimal.ONE.movePointLeft(scale))
+ .negate();
+
+ // Truncate input bounds, find the min value that can appear in
truncated output
+ BigDecimal minTrunc = minInput.divide(unit, 0,
RoundingMode.FLOOR).multiply(unit);
+ int finalPrecision = Math.max(minTrunc.precision(), precision);
+
+ return Types.DecimalType.of(finalPrecision, scale);
Review Comment:
Capping it might work, though for positive values, overflows are avoidable I
think, when `v - (v % W)` is used instead of `v - (((v % W) + W) % W)` for
positive values. Nevertheless, this sounds like a breaking change for me,
probably better to discuss it with community first?
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