postgres: improve snapshot-tests for long/wide situations (#84387)

pkg/tsdb/grafana-postgresql-datasource/postgres_snapshot_test.go

@@ -98,7 +98,8 @@ func TestIntegrationPostgresSnapshots(t *testing.T) {
 		format string
 	}{
 		{format: "time_series", name: "simple"},
-		{format: "time_series", name: "no_rows"},
+		{format: "time_series", name: "no_rows_long"},
+		{format: "time_series", name: "no_rows_wide"},
 		{format: "time_series", name: "7x_compat_metric_label"},
 		{format: "time_series", name: "convert_to_float64"},
 		{format: "time_series", name: "convert_to_float64_not"},

pkg/tsdb/grafana-postgresql-datasource/testdata/time_series/no_rows_wide.golden.jsonc

@@ -0,0 +1,36 @@
+//  🌟 This was machine generated.  Do not edit. 🌟
+//  
+//  Frame[0] {
+//      "typeVersion": [
+//          0,
+//          0
+//      ],
+//      "executedQueryString": "SELECT * FROM tbl WHERE false"
+//  }
+//  Name: 
+//  Dimensions: 0 Fields by 0 Rows
+//  +
+//  +
+//  
+//  
+//  🌟 This was machine generated.  Do not edit. 🌟
+{
+  "status": 200,
+  "frames": [
+    {
+      "schema": {
+        "meta": {
+          "typeVersion": [
+            0,
+            0
+          ],
+          "executedQueryString": "SELECT * FROM tbl WHERE false"
+        },
+        "fields": []
+      },
+      "data": {
+        "values": []
+      }
+    }
+  ]
+}

pkg/tsdb/grafana-postgresql-datasource/testdata/time_series/no_rows_wide.sql

@@ -0,0 +1,10 @@
+-- SELECT * FROM tbl WHERE false
+CREATE TEMPORARY TABLE tbl (
+    "time" timestamp with time zone,
+    v1 double precision,
+    v2 double precision
+);
+
+INSERT INTO tbl ("time", v1, v2) VALUES
+('2023-12-24 14:30:03 UTC', 10, 110),
+('2023-12-24 14:31:03 UTC', 20, 120);