zach comments

go/libraries/doltcore/sqle/kvexec/builder.go

@@ -59,16 +59,14 @@ func (b Builder) Build(ctx *sql.Context, n sql.Node, r sql.Row) (sql.RowIter, er
 			}
 		}
 	case *plan.GroupBy:
-		// no grouping
-		// only COUNT expression
-		// table or ita as child
-		// simple count expression
-		// no filter
 		if len(n.GroupByExprs) == 0 && len(n.SelectedExprs) == 1 {
 			if cnt, ok := n.SelectedExprs[0].(*aggregation.Count); ok {
 				if _, srcIter, _, srcSchema, _, srcFilter, err := getSourceKv(ctx, n.Child, true); err == nil && srcSchema != nil && srcFilter == nil {
 					iter, ok, err := newCountAggregationKvIter(srcIter, srcSchema, cnt.Child)
 					if ok && err == nil {
+						// (1) no grouping expressions (returns one row)
+						// (2) only one COUNT expression with a literal or field reference
+						// (3) table or ita as child (no filters)
 						return iter, nil
 					}
 				}

go/libraries/doltcore/sqle/kvexec/count_agg.go

@@ -81,6 +81,8 @@ func (l *countAggKvIter) Next(ctx *sql.Context) (sql.Row, error) {
 		k, v, err := l.srcIter.Next(ctx)
 		if err == io.EOF {
 			break
+		} else if err != nil {
+			return nil, err
 		}
 		if l.nullable {
 			if l.isKeyRef && k.FieldIsNull(l.idx) ||

go/libraries/doltcore/sqle/kvexec/count_agg_test.go

@@ -80,7 +80,7 @@ func TestCountAgg(t *testing.T) {
 			doRowexec: true,
 		},
 		{
-			name: "reject complex count expressi	on",
+			name: "reject complex count expression",
 			setup: []string{
 				"create table xy (x int primary key, y int, key y_idx(y))",
 			},