add compatibility code to handle pre 5.3 usage

pkg/tsdb/postgres/macros.go

@@ -30,6 +30,23 @@ func (m *postgresMacroEngine) Interpolate(query *tsdb.Query, timeRange *tsdb.Tim
 	var macroError error
 
 	sql = replaceAllStringSubmatchFunc(rExp, sql, func(groups []string) string {
+
+		// detect if $__timeGroup is supposed to add AS time for pre 5.3 compatibility
+		// if there is a ',' directly after the macro call $__timeGroup is probably used
+		// in the old way. Inside window function ORDER BY $__timeGroup will be followed
+		// by ')'
+		if groups[1] == "__timeGroup" {
+			if index := strings.Index(sql, groups[0]); index >= 0 {
+				index += len(groups[0])
+				if len(sql) > index {
+					// check for character after macro expression
+					if sql[index] == ',' {
+						groups[1] = "__timeGroupAlias"
+					}
+				}
+			}
+		}
+
 		args := strings.Split(groups[2], ",")
 		for i, arg := range args {
 			args[i] = strings.Trim(arg, " ")