fix: fill empty metrics data with zeros

Signed-off-by: huanggze <loganhuang@yunify.com>

pkg/models/metrics/metricsruleconst.go

@@ -13,6 +13,10 @@ limitations under the License.
 
 package metrics
 
+import (
+	"fmt"
+)
+
 const (
 	ResultTypeVector             = "vector"
 	ResultTypeMatrix             = "matrix"
@@ -731,3 +735,11 @@ var RulePromQLTmplMap = MetricMap{
 	"prometheus_up_sum":                          `prometheus:up:sum`,
 	"prometheus_tsdb_head_samples_appended_rate": `prometheus:prometheus_tsdb_head_samples_appended:sum_rate`,
 }
+
+func init() {
+	for metric, promql := range RulePromQLTmplMap {
+
+		// Use absent() to fill missing data with zero
+		RulePromQLTmplMap[metric] = fmt.Sprintf("%s or absent(%s)-1", promql, promql)
+	}
+}