Fixed the below review comments given by Ashesh Vashi

    Instead of having db version string from yml file, user can define the range of
    database server version where query is to be executed.

    If user want to run the query on database version greater than 10.0.0, use below format.
      runonserver: ">=10.0.0"

      Below are the example of db version range user can defined in yml file.
            <=10.1.0
            >=12.1.0
            =11.0.0
            <9.6.0 || >=11.0.0

Author: neel5481

cmd/postgres_exporter/postgres_exporter.go

@@ -224,7 +224,7 @@ var builtinMetricMaps = map[string]intermediateMetricMap{
 		},
 		true,
 		0,
-		"all",
+		"",
 	},
 	"pg_stat_database": {
 		map[string]ColumnMapping{
@@ -250,7 +250,7 @@ var builtinMetricMaps = map[string]intermediateMetricMap{
 		},
 		true,
 		0,
-		"all",
+		"",
 	},
 	"pg_stat_database_conflicts": {
 		map[string]ColumnMapping{
@@ -264,7 +264,7 @@ var builtinMetricMaps = map[string]intermediateMetricMap{
 		},
 		true,
 		0,
-		"all",
+		"",
 	},
 	"pg_locks": {
 		map[string]ColumnMapping{
@@ -274,7 +274,7 @@ var builtinMetricMaps = map[string]intermediateMetricMap{
 		},
 		true,
 		0,
-		"all",
+		"",
 	},
 	"pg_stat_replication": {
 		map[string]ColumnMapping{
@@ -321,7 +321,7 @@ var builtinMetricMaps = map[string]intermediateMetricMap{
 		},
 		true,
 		0,
-		"all",
+		"",
 	},
 	"pg_stat_archiver": {
 		map[string]ColumnMapping{
@@ -336,7 +336,7 @@ var builtinMetricMaps = map[string]intermediateMetricMap{
 		},
 		true,
 		0,
-		"all",
+		"",
 	},
 	"pg_stat_activity": {
 		map[string]ColumnMapping{
@@ -347,7 +347,7 @@ var builtinMetricMaps = map[string]intermediateMetricMap{
 		},
 		true,
 		0,
-		"all",
+		"",
 	},
 }
 
@@ -504,7 +504,6 @@ func parseUserQueries(content []byte) (map[string]intermediateMetricMap, map[str
 		return nil, nil, err
 	}
 
-
 	// Stores the loaded map representation
 	metricMaps := make(map[string]intermediateMetricMap)
 	newQueryOverrides := make(map[string]string)
@@ -844,11 +843,10 @@ type cachedMetrics struct {
 // Server describes a connection to Postgres.
 // Also it contains metrics map and query overrides.
 type Server struct {
-	db     *sql.DB
-	labels prometheus.Labels
-	master bool
+	db          *sql.DB
+	labels      prometheus.Labels
+	master      bool
 	runonserver string
-	serverversion string
 
 	// Last version used to calculate metric map. If mismatch on scrape,
 	// then maps are recalculated.
@@ -894,7 +892,6 @@ func NewServer(dsn string, opts ...ServerOpt) (*Server, error) {
 	s := &Server{
 		db:     db,
 		master: false,
-		runonserver: "all",
 		labels: prometheus.Labels{
 			serverLabelName: fingerprint,
 		},
@@ -1342,10 +1339,14 @@ func queryNamespaceMappings(ch chan<- prometheus.Metric, server *Server) map[str
 			continue
 		}
 
-		// check if the query is to be run on specific server version or not
-		if len(mapping.runonserver) > 0 && !strings.Contains(mapping.runonserver, "all") && !strings.Contains(server.serverversion, mapping.runonserver) {
-			log.Debugln("Query skipped for database version: [%s] as it should be run on database server version: [%s]", server.serverversion, mapping.runonserver)
-			continue
+		// check if the query is to be run on specific database server version range or not
+		if len(mapping.runonserver) > 0 {
+			serVersion, _ := semver.Parse(server.lastMapVersion.String())
+			runServerRange, _ := semver.ParseRange(mapping.runonserver)
+			if !runServerRange(serVersion) {
+				log.Debugln("Query skipped for database version: [%s] as it should be run on database server version: [%s]", server.lastMapVersion.String(), mapping.runonserver)
+				continue
+			}
 		}
 
 		scrapeMetric := false
@@ -1436,7 +1437,6 @@ func (e *Exporter) checkMapVersions(ch chan<- prometheus.Metric, server *Server)
 		}
 
 		server.lastMapVersion = semanticVersion
-		server.serverversion = semanticVersion.String()
 
 		if e.userQueriesPath != "" {
 			// Clear the metric while a reload is happening