[GitHub] [hive] soumyakanti3578 commented on a change in pull request #2360: [HIVE-25209]SELECT query with SUM function producing unexpected result

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soumyakanti3578 commented on a change in pull request #2360:
URL: https://github.com/apache/hive/pull/2360#discussion_r656373540



##########
File path: ql/src/java/org/apache/hadoop/hive/ql/optimizer/StatsOptimizer.java
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@@ -397,6 +397,11 @@ else if (getGbyKeyType(cgbyOp) == GbyKeyType.CONSTANT && 
rowCnt == 0) {
           if (udaf instanceof GenericUDAFSum) {
             // long/double/decimal
             ExprNodeDesc desc = aggr.getParameters().get(0);
+            // return null for SUM(1), when the table is empty. Without this, 
category = LONG, and the result is 0
+            // instead of NULL.
+            if (desc instanceof ExprNodeConstantDesc && rowCnt == 0) {
+              return null;

Review comment:
       Do you mean, instead of returning null, I should return oneRow.add(null) 
?




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