diff --git a/server/internal/api/exports.go b/server/internal/api/exports.go
index 5494fee..15acdb9 100644
--- a/server/internal/api/exports.go
+++ b/server/internal/api/exports.go
@@ -305,8 +305,18 @@ func (a *ExportsAPI) create(w http.ResponseWriter, r *http.Request) {
 		fail(w, r, http.StatusBadRequest, fmt.Sprintf("EXPLAIN 未通过：评分=%d，请优化索引或缩小查询范围", score))
 		return
 	}
+	// 估算行数（优先使用分块统计，失败或结果为 0 时回退到单次 COUNT）
 	var estimate int64
 	estimate = rrepo.EstimateFastChunked(dataDB, ds, main, p.Filters)
+	if estimate <= 0 {
+		logging.JSON("WARN", map[string]interface{}{
+			"event":      "estimate_zero_fallback",
+			"datasource": ds,
+			"main_table": main,
+			"filters":    p.Filters,
+		})
+		estimate = rrepo.EstimateFast(dataDB, ds, main, p.Filters)
+	}
 	hdrs := make([]string, len(filtered))
 	for i, tf := range filtered {
 		if v, ok := labels[tf]; ok {