fix(exports): 优化导出逻辑以支持动态时间范围分片

- 在 CountRowsFastChunked 函数中添加时间跨度计算，支持根据时间跨度选择按天或按周分片
- 新增 SplitByWeeks 函数以实现按周分割时间范围
- 增强日志记录，提供分片信息以便于后续分析和调试

server/internal/exporter/stream.go

@@ -195,7 +195,30 @@ func CountRowsFastChunked(db *sql.DB, ds, main string, filters map[string]interf
 	if start == "" || end == "" {
 		return CountRowsFast(db, ds, main, filters)
 	}
-	ranges := SplitByDays(start, end, 15)
+	// 计算时间跨度（天数）
+	layout := "2006-01-02 15:04:05"
+	st, err1 := time.Parse(layout, start)
+	en, err2 := time.Parse(layout, end)
+	if err1 != nil || err2 != nil {
+		return CountRowsFast(db, ds, main, filters)
+	}
+	daysDiff := int(en.Sub(st).Hours() / 24)
+	
+	// 如果时间跨度超过 15 天（半个月），使用按周分片（7天），否则使用按天分片（15天）
+	var ranges [][2]string
+	if daysDiff > 15 {
+		ranges = SplitByWeeks(start, end)
+		logging.JSON("INFO", map[string]interface{}{
+			"event":      "count_chunked_by_weeks",
+			"datasource": ds,
+			"main":       main,
+			"days_diff":  daysDiff,
+			"chunks":     len(ranges),
+		})
+	} else {
+		ranges = SplitByDays(start, end, 15)
+	}
+	
 	var total int64
 	for _, rg := range ranges {
 		fl := map[string]interface{}{}
@@ -232,6 +255,30 @@ func SplitByDays(startStr, endStr string, stepDays int) [][2]string {
 	return out
 }
 
+// SplitByWeeks 按周（7天）分割时间范围，返回多个时间区间
+func SplitByWeeks(startStr, endStr string) [][2]string {
+	layout := "2006-01-02 15:04:05"
+	s := strings.TrimSpace(startStr)
+	e := strings.TrimSpace(endStr)
+	st, err1 := time.Parse(layout, s)
+	en, err2 := time.Parse(layout, e)
+	if err1 != nil || err2 != nil || !en.After(st) {
+		return [][2]string{{s, e}}
+	}
+	var out [][2]string
+	cur := st
+	weekDuration := 7 * 24 * time.Hour
+	for cur.Before(en) {
+		nxt := cur.Add(weekDuration)
+		if nxt.After(en) {
+			nxt = en
+		}
+		out = append(out, [2]string{cur.Format(layout), nxt.Format(layout)})
+		cur = nxt
+	}
+	return out
+}
+
 type RowTransform func([]string) []string
 type RollCallback func(path string, size int64, partRows int64) error
 type ProgressCallback func(totalRows int64) error