PostgreSQL: __unixEpochGroup to support arithmetic expression as argument (#46764)

* __unixEpochGroup to support arithmetic argument

Following call generates wrong expression : 
 
$__unixEpochGroupAlias(height+42,$__interval)

=> floor(height+42/60)*60 AS "time"

instead of

=> floor((height+42)/60)*60 AS "time"

* Update test of __unixEpochGroup related to issue #46764

pkg/tsdb/postgres/macros.go

@@ -146,7 +146,7 @@ func (m *postgresMacroEngine) evaluateMacro(timeRange backend.TimeRange, query *
 				return "", err
 			}
 		}
-		return fmt.Sprintf("floor(%s/%v)*%v", args[0], interval.Seconds(), interval.Seconds()), nil
+		return fmt.Sprintf("floor((%s)/%v)*%v", args[0], interval.Seconds(), interval.Seconds()), nil
 	case "__unixEpochGroupAlias":
 		tg, err := m.evaluateMacro(timeRange, query, "__unixEpochGroup", args)
 		if err == nil {

pkg/tsdb/postgres/macros_test.go

@@ -137,11 +137,11 @@ func TestMacroEngine(t *testing.T) {
 		})
 
 		t.Run("interpolate __unixEpochGroup function", func(t *testing.T) {
-			sql, err := engine.Interpolate(query, timeRange, "SELECT $__unixEpochGroup(time_column,'5m')")
+			sql, err := engine.Interpolate(query, timeRange, "SELECT $__unixEpochGroup(time_column+time_adjustment,'5m')")
 			require.NoError(t, err)
-			sql2, err := engine.Interpolate(query, timeRange, "SELECT $__unixEpochGroupAlias(time_column,'5m')")
+			sql2, err := engine.Interpolate(query, timeRange, "SELECT $__unixEpochGroupAlias(time_column+time_adjustment,'5m')")
 			require.NoError(t, err)
-			require.Equal(t, "SELECT floor(time_column/300)*300", sql)
+			require.Equal(t, "SELECT floor((time_column+time_adjustment)/300)*300", sql)
 			require.Equal(t, sql2, sql+" AS \"time\"")
 		})
 	})