Fix taosdemo test failure

tests/pytest/tools/taosdemoTest2.py

@@ -31,10 +31,18 @@ class TDTestCase:
 
     def insertDataAndAlterTable(self, threadID):
         if(threadID == 0):
-            os.system("yes | taosdemo -t %d -n %d" % (self.numberOfTables, self.numberOfRecords))
+            os.system("yes | taosdemo -t %d -n %d -x" % (self.numberOfTables, self.numberOfRecords))
         if(threadID == 1):
             print("use test")
             tdSql.execute("use test")
+            while True:
+                print("query started")
+                tdSql.query("select * from test.t9")
+                rows = tdSql.queryRows
+                print("rows %d" % rows)
+                if(rows > 0):
+                    break
+                time.sleep(1)      
             print("alter table test.meters add column f4 int")
             tdSql.execute("alter table test.meters add column f4 int")
             print("insert into test.t0 values (now, 1, 2, 3, 4)")