[v9.5.x] InfluxDB: Fix adding FROM statement when the measurement is an empty string (#67835)

InfluxDB: Fix adding FROM statement when the measurement is an empty string (#67827)

* If the measurement empty don't add FROM statement

* Add comment line

(cherry picked from commit 764f87b485)

Co-authored-by: ismail simsek <ismailsimsek09@gmail.com>

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

@@ -64,7 +64,8 @@ export class InfluxQueryBuilder {
       measurement = this.target.measurement;
       policy = this.target.policy;
 
-      if (!measurement.match('^/.*/')) {
+      // If there is a measurement and it is not empty string
+      if (!measurement.match(/^\/.*\/|^$/)) {
         measurement = '"' + measurement + '"';
 
         if (policy && policy !== 'default') {
@@ -73,6 +74,10 @@ export class InfluxQueryBuilder {
         }
       }
 
+      if (measurement === '') {
+        return 'SHOW FIELD KEYS';
+      }
+
       return 'SHOW FIELD KEYS FROM ' + measurement;
     } else if (type === 'RETENTION POLICIES') {
       query = 'SHOW RETENTION POLICIES on "' + this.database + '"';
@@ -89,7 +94,9 @@ export class InfluxQueryBuilder {
         measurement = policy + '.' + measurement;
       }
 
-      query += ' FROM ' + measurement;
+      if (measurement !== '') {
+        query += ' FROM ' + measurement;
+      }
     }
 
     if (withKey) {

public/app/plugins/datasource/influxdb/specs/query_builder.test.ts

@@ -213,5 +213,13 @@ describe('InfluxQueryBuilder', () => {
       const query = builder.buildExploreQuery('TAG_KEYS');
       expect(query).toBe(`SHOW TAG KEYS WHERE "app" == ''`);
     });
+
+    it('should not add FROM statement if the measurement empty', () => {
+      const builder = new InfluxQueryBuilder({ measurement: '', tags: [] });
+      let query = builder.buildExploreQuery('TAG_KEYS');
+      expect(query).toBe('SHOW TAG KEYS');
+      query = builder.buildExploreQuery('FIELDS');
+      expect(query).toBe('SHOW FIELD KEYS');
+    });
   });
 });