postgres: change $__timeGroup macro to include "AS time" column alias (#10119)

* change $__timeGroup macro to include column alias

* update docs and help text for $__timeGroup macro

docs/sources/features/datasources/postgres.md

@@ -48,7 +48,7 @@ Macro example | Description
 *$__timeFilter(dateColumn)* | Will be replaced by a time range filter using the specified column name. For example, *extract(epoch from dateColumn) BETWEEN 1494410783 AND 1494497183*
 *$__timeFrom()* | Will be replaced by the start of the currently active time selection. For example, *to_timestamp(1494410783)*
 *$__timeTo()* | Will be replaced by the end of the currently active time selection. For example, *to_timestamp(1494497183)*
-*$__timeGroup(dateColumn,'5m')* | Will be replaced by an expression usable in GROUP BY clause. For example, *(extract(epoch from "dateColumn")/300)::bigint*300*
+*$__timeGroup(dateColumn,'5m')* | Will be replaced by an expression usable in GROUP BY clause. For example, *(extract(epoch from dateColumn)/300)::bigint*300 AS time*
 *$__unixEpochFilter(dateColumn)* | Will be replaced by a time range filter using the specified column name with times represented as unix timestamp. For example, *dateColumn > 1494410783 AND dateColumn < 1494497183*
 *$__unixEpochFrom()* | Will be replaced by the start of the currently active time selection as unix timestamp. For example, *1494410783*
 *$__unixEpochTo()* | Will be replaced by the end of the currently active time selection as unix timestamp. For example, *1494497183*
@@ -94,7 +94,7 @@ Example with `metric` column
 
 ```sql
 SELECT
-  $__timeGroup(time_date_time,'5m') as time,
+  $__timeGroup(time_date_time,'5m'),
   min(value_double),
   'min' as metric
 FROM test_data
@@ -107,7 +107,7 @@ Example with multiple columns:
 
 ```sql
 SELECT
-  $__timeGroup(time_date_time,'5m') as time,
+  $__timeGroup(time_date_time,'5m'),
   min(value_double) as min_value,
   max(value_double) as max_value
 FROM test_data

pkg/tsdb/postgres/macros.go

@@ -89,7 +89,7 @@ func (m *PostgresMacroEngine) evaluateMacro(name string, args []string) (string,
 		if err != nil {
 			return "", fmt.Errorf("error parsing interval %v", args[1])
 		}
-		return fmt.Sprintf("(extract(epoch from \"%s\")/%v)::bigint*%v", args[0], interval.Seconds(), interval.Seconds()), nil
+		return fmt.Sprintf("(extract(epoch from %s)/%v)::bigint*%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

@@ -45,7 +45,7 @@ func TestMacroEngine(t *testing.T) {
 			sql, err := engine.Interpolate(timeRange, "GROUP BY $__timeGroup(time_column,'5m')")
 			So(err, ShouldBeNil)
 
-			So(sql, ShouldEqual, "GROUP BY (extract(epoch from \"time_column\")/300)::bigint*300")
+			So(sql, ShouldEqual, "GROUP BY (extract(epoch from time_column)/300)::bigint*300 AS time")
 		})
 
 		Convey("interpolate __timeTo function", func() {

public/app/plugins/datasource/postgres/partials/query.editor.html

@@ -50,11 +50,11 @@ Macros:
 - $__timeEpoch -> extract(epoch from column) as "time"
 - $__timeFilter(column) ->  extract(epoch from column) BETWEEN 1492750877 AND 1492750877
 - $__unixEpochFilter(column) ->  column > 1492750877 AND column < 1492750877
-- $__timeGroup(column,'5m') -> (extract(epoch from "dateColumn")/300)::bigint*300
+- $__timeGroup(column,'5m') -> (extract(epoch from column)/300)::bigint*300 AS time
 
 Example of group by and order by with $__timeGroup:
 SELECT
-  $__timeGroup(date_time_col, '1h') AS time,
+  $__timeGroup(date_time_col, '1h'),
   sum(value) as value
 FROM yourtable
 GROUP BY time