Fix incorrect YAML test assertion and add datarows validation

- Fix total count from 3 to 2 in YAML REST test (bin+chart with
  category produces 2 groups, not 3)
- Add datarows assertions to both YAML test cases for row-level
  validation
- Correct table statistics row count in unit test

Signed-off-by: Heng Qian <qianheng@amazon.com>

Author: qianheng-aws

integ-test/src/yamlRestTest/resources/rest-api-spec/test/issues/5174.yml

@@ -62,8 +62,9 @@ teardown:
         body:
           query: source=issue5174 | bin value span=50 as val_bin | chart count() over val_bin by category
 
-  - match: { total: 3 }
+  - match: { total: 2 }
   - match: { schema: [ { name: val_bin, type: string }, { name: category, type: string }, { name: "count()", type: bigint } ] }
+  - match: { datarows: [ [ "0-50", "A", 2 ], [ "100-150", "B", 1 ] ] }
 
 ---
 "Issue 5174: bin then chart with single group and null values":
@@ -79,3 +80,4 @@ teardown:
 
   - match: { total: 2 }
   - match: { schema: [ { name: val_bin, type: string }, { name: "count()", type: bigint } ] }
+  - match: { datarows: [ [ "0-50", 2 ], [ "100-150", 1 ] ] }

ppl/src/test/java/org/opensearch/sql/ppl/calcite/CalcitePPLChartNullTest.java

@@ -145,7 +145,7 @@ public RelDataType getRowType(RelDataTypeFactory typeFactory) {
 
     @Override
     public Statistic getStatistic() {
-      return Statistics.of(0d, ImmutableList.of(), RelCollations.createSingleton(0));
+      return Statistics.of(4d, ImmutableList.of(), RelCollations.createSingleton(0));
     }
 
     @Override