[TD-4017]<test>: add test case

tests/pytest/query/unionAllTest.py

@@ -74,6 +74,16 @@ class TDTestCase:
 
         tdSql.error("select 'dc' as options from stb where type = 1 limit 1 union all select 'ad' as city from stb where type = 2 limit 1")
 
+        # for defect https://jira.taosdata.com:18080/browse/TD-4017
+        tdSql.execute("alter table stb add column col int")
+        tdSql.execute("insert into tb1 values(%d, 'option1', 'beijing', 10)" % (self.ts + 1000))
+
+        tdSql.query("select 'dc' as options from stb where col > 10 limit 1")
+        tdSql.checkRows(0)
+
+        tdSql.query("select 'dcs' as options from stb where col > 200 limit 1 union all select 'aaa' as options from stb limit 10")
+        tdSql.checkData(0, 0, 'aaa')
+
     def stop(self):
         tdSql.close()
         tdLog.success("%s successfully executed" % __file__)