[postgres] fix timeGroup macro rounding (#12468)

* fix timeGroup tests to check for correct grouping

* do explicit floor rounding in $__timeGroup macro

* fix typo in comments

pkg/tsdb/postgres/macros.go

@@ -109,7 +109,7 @@ func (m *PostgresMacroEngine) evaluateMacro(name string, args []string) (string,
 				m.Query.Model.Set("fillValue", floatVal)
 			}
 		}
-		return fmt.Sprintf("(extract(epoch from %s)/%v)::bigint*%v AS time", args[0], interval.Seconds(), interval.Seconds()), nil
+		return fmt.Sprintf("floor(extract(epoch from %s)/%v)*%v AS time", args[0], interval.Seconds(), interval.Seconds()), nil
 	case "__unixEpochFilter":
 		if len(args) == 0 {
 			return "", fmt.Errorf("missing time column argument for macro %v", name)

pkg/tsdb/postgres/macros_test.go

@@ -53,7 +53,7 @@ func TestMacroEngine(t *testing.T) {
 				sql, err := engine.Interpolate(query, timeRange, "GROUP BY $__timeGroup(time_column,'5m')")
 				So(err, ShouldBeNil)
 
-				So(sql, ShouldEqual, "GROUP BY (extract(epoch from time_column)/300)::bigint*300 AS time")
+				So(sql, ShouldEqual, "GROUP BY floor(extract(epoch from time_column)/300)*300 AS time")
 			})
 
 			Convey("interpolate __timeGroup function with spaces between args", func() {
@@ -61,7 +61,7 @@ func TestMacroEngine(t *testing.T) {
 				sql, err := engine.Interpolate(query, timeRange, "GROUP BY $__timeGroup(time_column , '5m')")
 				So(err, ShouldBeNil)
 
-				So(sql, ShouldEqual, "GROUP BY (extract(epoch from time_column)/300)::bigint*300 AS time")
+				So(sql, ShouldEqual, "GROUP BY floor(extract(epoch from time_column)/300)*300 AS time")
 			})
 
 			Convey("interpolate __timeTo function", func() {

pkg/tsdb/postgres/postgres_test.go

@@ -189,21 +189,23 @@ func TestPostgres(t *testing.T) {
 				So(queryResult.Error, ShouldBeNil)
 
 				points := queryResult.Series[0].Points
-				So(len(points), ShouldEqual, 6)
+				// without fill this should result in 4 buckets
+				So(len(points), ShouldEqual, 4)
 
 				dt := fromStart
 
-				for i := 0; i < 3; i++ {
+				for i := 0; i < 2; i++ {
 					aValue := points[i][0].Float64
 					aTime := time.Unix(int64(points[i][1].Float64)/1000, 0)
 					So(aValue, ShouldEqual, 15)
 					So(aTime, ShouldEqual, dt)
+					So(aTime.Unix()%300, ShouldEqual, 0)
 					dt = dt.Add(5 * time.Minute)
 				}
 
-				// adjust for 5 minute gap
-				dt = dt.Add(5 * time.Minute)
-				for i := 3; i < 6; i++ {
+				// adjust for 10 minute gap between first and second set of points
+				dt = dt.Add(10 * time.Minute)
+				for i := 2; i < 4; i++ {
 					aValue := points[i][0].Float64
 					aTime := time.Unix(int64(points[i][1].Float64)/1000, 0)
 					So(aValue, ShouldEqual, 20)
@@ -239,7 +241,7 @@ func TestPostgres(t *testing.T) {
 
 				dt := fromStart
 
-				for i := 0; i < 3; i++ {
+				for i := 0; i < 2; i++ {
 					aValue := points[i][0].Float64
 					aTime := time.Unix(int64(points[i][1].Float64)/1000, 0)
 					So(aValue, ShouldEqual, 15)
@@ -247,17 +249,23 @@ func TestPostgres(t *testing.T) {
 					dt = dt.Add(5 * time.Minute)
 				}
 
+				// check for NULL values inserted by fill
+				So(points[2][0].Valid, ShouldBeFalse)
 				So(points[3][0].Valid, ShouldBeFalse)
 
-				// adjust for 5 minute gap
-				dt = dt.Add(5 * time.Minute)
-				for i := 4; i < 7; i++ {
+				// adjust for 10 minute gap between first and second set of points
+				dt = dt.Add(10 * time.Minute)
+				for i := 4; i < 6; i++ {
 					aValue := points[i][0].Float64
 					aTime := time.Unix(int64(points[i][1].Float64)/1000, 0)
 					So(aValue, ShouldEqual, 20)
 					So(aTime, ShouldEqual, dt)
 					dt = dt.Add(5 * time.Minute)
 				}
+
+				// check for NULL values inserted by fill
+				So(points[6][0].Valid, ShouldBeFalse)
+
 			})
 
 			Convey("When doing a metric query using timeGroup with float fill enabled", func() {