fix: add flag to ignore results with missing values

cmd/sql_exporter/main.go

@@ -41,6 +41,7 @@ var (
 func init() {
 	prometheus.MustRegister(version.NewCollector("sql_exporter"))
 	flag.BoolVar(&cfg.EnablePing, "config.enable-ping", true, "Enable ping for targets")
+	flag.BoolVar(&cfg.IgnoreMissingVals, "config.ignore-missing-values", false, "[EXPERIMENTAL] Ignore results with missing values for the requested columns")
 	flag.StringVar(&cfg.DsnOverride, "config.data-source-name", "", "Data source name to override the value in the configuration file with")
 	flag.StringVar(&cfg.TargetLabel, "config.target-label", "target", "Target label name")
 }

config/config.go

@@ -26,9 +26,10 @@ const EnvDsnOverride = "SQLEXPORTER_TARGET_DSN"
 const MaxInt32 int = 1<<31 - 1
 
 var (
-	EnablePing  bool
-	DsnOverride string
-	TargetLabel string
+	EnablePing        bool
+	IgnoreMissingVals bool
+	DsnOverride       string
+	TargetLabel       string
 )
 
 // Load attempts to parse the given config file and return a Config object.

query.go

@@ -89,6 +89,10 @@ func (q *Query) Collect(ctx context.Context, conn *sql.DB, ch chan<- Metric) {
 
 	dest, err := q.scanDest(rows)
 	if err != nil {
+		if config.IgnoreMissingVals {
+			klog.V(3).Info(err)
+			return
+		}
 		ch <- NewInvalidMetric(err)
 		return
 	}