influxdb: adds mode func to backend

closes #12286

pkg/tsdb/influxdb/query_part.go

@@ -31,6 +31,7 @@ func init() {
 	renders["mean"] = QueryDefinition{Renderer: functionRenderer}
 	renders["median"] = QueryDefinition{Renderer: functionRenderer}
 	renders["sum"] = QueryDefinition{Renderer: functionRenderer}
+	renders["mode"] = QueryDefinition{Renderer: functionRenderer}
 
 	renders["holt_winters"] = QueryDefinition{
 		Renderer: functionRenderer,

pkg/tsdb/influxdb/query_part_test.go

@@ -84,5 +84,13 @@ func TestInfluxdbQueryPart(t *testing.T) {
 			res := part.Render(query, queryContext, "distinct(value)")
 			So(res, ShouldEqual, `count(distinct(value))`)
 		})
+
+		Convey("render mode", func() {
+			part, err := NewQueryPart("mode", []string{})
+			So(err, ShouldBeNil)
+
+			res := part.Render(query, queryContext, "value")
+			So(res, ShouldEqual, `mode(value)`)
+		})
 	})
 }