pgsql: Reduce cost of GetNotification by 2.5

By delaying the Layer join to the very end, we can cut the query costs from 540,836 to 219,477.

See Pull Request for details.

database/pgsql/queries.go

@@ -211,23 +211,21 @@ const (
 		WHERE name = $1`
 
 	searchNotificationLayerIntroducingVulnerability = `
-	WITH subquery AS (
-		SELECT l.ID, l.name
-		FROM Vulnerability_Affects_FeatureVersion vafv, FeatureVersion fv, Layer_diff_FeatureVersion ldfv, Layer l
-		WHERE l.id >= $2
-			AND vafv.vulnerability_id = $1
-			AND vafv.featureversion_id = fv.id
-			AND ldfv.featureversion_id = fv.id
-			AND ldfv.modification = 'add'
-			AND ldfv.layer_id = l.id
-		ORDER BY l.ID
-	)
-
-	SELECT *
-	FROM subquery
-	LIMIT $3;
-`
-
+		WITH LDFV AS (
+		  SELECT ldfv.layer_id
+		  FROM Vulnerability_Affects_FeatureVersion vafv, FeatureVersion fv, Layer_diff_FeatureVersion ldfv
+		  WHERE ldfv.layer_id >= $2
+		    AND vafv.vulnerability_id = $1
+		    AND vafv.featureversion_id = fv.id
+		    AND ldfv.featureversion_id = fv.id
+		    AND ldfv.modification = 'add'
+		  ORDER BY ldfv.ID
+		)
+		SELECT l.id, l.name
+		FROM LDFV, Layer l
+		WHERE LDFV.layer_id = l.id
+		LIMIT $3`
+
 	// complex_test.go
 	searchComplexTestFeatureVersionAffects = `
 		SELECT v.name