best practices in examples

examples/pagination/cities.go

@@ -68,9 +68,16 @@
 				_ = res.Close()
 			}()
 			if !res.NextResultSet(ctx) || !res.HasNextRow() {
-				empty = true
+				if err := ctx.Err(); err != nil {
+					return err
+				}
 
-				return res.Err()
+				if err := res.Err(); err != nil {
+					return err
+				}
+
+				empty = true
+				return nil
 			}
 			var addr string
 			for res.NextRow() {

examples/serverless/url_shortener/service.go

@@ -304,6 +304,14 @@ func (s *service) selectLong(ctx context.Context, hash string) (url string, err
 		}
 	}
 
+	if err := ctx.Err(); err != nil {
+		return "", err
+	}
+
+	if err := res.Err(); err != nil {
+		return "", err
+	}
+
 	return "", fmt.Errorf("hash '%s' is not found", hash)
 }
 

examples/topic/cdc-cache-bus-freeseats/webserver.go

@@ -182,7 +182,9 @@ func (s *server) IndexPageHandler(writer http.ResponseWriter, request *http.Requ
 			return err
 		}
 
-		res.NextResultSet(ctx, "id")
+		if err := res.NextResultSetErr(ctx, "id"); err != nil {
+			return err
+		}
 
 		for res.HasNextRow() {
 			res.NextRow()
@@ -194,7 +196,7 @@ func (s *server) IndexPageHandler(writer http.ResponseWriter, request *http.Requ
 			busIDs = append(busIDs, id)
 		}
 
-		return nil
+		return res.Err()
 	})
 	if err != nil {
 		http.Error(writer, err.Error(), http.StatusInternalServerError)

examples/ttl/series.go

@@ -123,8 +123,18 @@
 				_ = res.Close()
 			}()
 
-			empty = true
-			res.NextResultSet(ctx)
+			if !res.NextResultSet(ctx) || !res.HasNextRow() {
+				if err := ctx.Err(); err != nil {
+					return err
+				}
+
+				if err := res.Err(); err != nil {
+					return err
+				}
+
+				empty = true
+				return nil
+			}
 			for res.NextRow() {
 				empty = false
 				err = res.ScanNamed(