fix(influxdb): removes quotes for field key queries

fixes #6473

public/app/plugins/datasource/influxdb/query_builder.js

@@ -56,8 +56,11 @@ function (_) {
         query += ' WITH MEASUREMENT =~ /' + withMeasurementFilter +'/';
       }
     } else if (type === 'FIELDS') {
-      query = 'SHOW FIELD KEYS FROM "' + this.target.measurement + '"';
-      return query;
+      if (!this.target.measurement.match('^/.*/')) {
+        return 'SHOW FIELD KEYS FROM "' + this.target.measurement + '"';
+      } else {
+        return 'SHOW FIELD KEYS FROM ' + this.target.measurement;
+      }
     } else if (type === 'RETENTION POLICIES') {
       query = 'SHOW RETENTION POLICIES on "' + this.database + '"';
       return query;

public/app/plugins/datasource/influxdb/specs/query_builder_specs.ts

@@ -88,6 +88,12 @@ describe('InfluxQueryBuilder', function() {
       expect(query).to.be('SHOW FIELD KEYS FROM "cpu"');
     });
 
+    it('should build show field query with regexp', function() {
+      var builder = new InfluxQueryBuilder({measurement: '/$var/', tags: [{key: 'app', value: 'email'}]});
+      var query = builder.buildExploreQuery('FIELDS');
+      expect(query).to.be('SHOW FIELD KEYS FROM /$var/');
+    });
+
     it('should build show retention policies query', function() {
       var builder = new InfluxQueryBuilder({measurement: 'cpu', tags: []}, 'site');
       var query = builder.buildExploreQuery('RETENTION POLICIES');