[GitHub] [flink] lsyldliu commented on a diff in pull request #22031: [FLINK-31239][hive] Fix native sum function can't get the corrected value when the argument type is string

["lsyldliu (via GitHub)" <gi...@apache.org>]

lsyldliu commented on code in PR #22031:
URL: https://github.com/apache/flink/pull/22031#discussion_r1123961288


##########
flink-connectors/flink-connector-hive/src/main/java/org/apache/flink/table/functions/hive/HiveSumAggFunction.java:
##########
@@ -88,27 +97,27 @@ public Expression[] retractExpressions() {
 
     @Override
     public Expression[] mergeExpressions() {
+        Expression coalesceSum = coalesce(sum, zero);
         return new Expression[] {
             /* sum = */ ifThenElse(
                     isNull(mergeOperand(sum)),
-                    sum,
-                    ifThenElse(
-                            isNull(sum),
-                            mergeOperand(sum),
-                            adjustedPlus(getResultType(), sum, mergeOperand(sum))))
+                    coalesceSum,
+                    adjustedPlus(getResultType(), coalesceSum, mergeOperand(sum))),
+            and(isEmpty, mergeOperand(isEmpty))
         };
     }
 
     @Override
     public Expression getValueExpression() {
-        return sum;
+        return ifThenElse(isTrue(isEmpty), nullOf(getResultType()), sum);

Review Comment:
   Hive code as following: 
   ```
   @AggregationType(estimable = true)
       static class SumLongAgg extends SumAgg<Long> {
         @Override
         public int estimate() { return JavaDataModel.PRIMITIVES1 + JavaDataModel.PRIMITIVES2; }
       }
   
       @Override
       public AggregationBuffer getNewAggregationBuffer() throws HiveException {
         SumLongAgg result = new SumLongAgg();
         reset(result);
         return result;
       }
   
       @Override
       public void reset(AggregationBuffer agg) throws HiveException {
         SumLongAgg myagg = (SumLongAgg) agg;
         myagg.empty = true;
         myagg.sum = 0L;
         myagg.uniqueObjects = new HashSet<ObjectInspectorObject>();
       }
   
       private boolean warned = false;
   
       @Override
       public void iterate(AggregationBuffer agg, Object[] parameters) throws HiveException {
         assert (parameters.length == 1);
         try {
           if (isEligibleValue((SumLongAgg) agg, parameters[0])) {
             ((SumLongAgg)agg).empty = false;
             ((SumLongAgg)agg).sum += PrimitiveObjectInspectorUtils.getLong(parameters[0], inputOI);
           }
         } catch (NumberFormatException e) {
           if (!warned) {
             warned = true;
             LOG.warn(getClass().getSimpleName() + " "
                 + StringUtils.stringifyException(e));
           }
         }
       }
   
       @Override
       public void merge(AggregationBuffer agg, Object partial) throws HiveException {
         if (partial != null) {
           SumLongAgg myagg = (SumLongAgg) agg;
           myagg.empty = false;
           if (isWindowingDistinct()) {
             throw new HiveException("Distinct windowing UDAF doesn't support merge and terminatePartial");
           } else {
               myagg.sum += PrimitiveObjectInspectorUtils.getLong(partial, inputOI);
           }
         }
       }
   
       @Override
       public Object terminate(AggregationBuffer agg) throws HiveException {
         SumLongAgg myagg = (SumLongAgg) agg;
         if (myagg.empty) {
           return null;
         }
         result.set(myagg.sum);
         return result;
       }
   ```
   It returns a null value if all elements are null.



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