[TD-1389] <test>: Update null value test

tests/pytest/query/queryNormal.py

@@ -42,6 +42,8 @@ class TDTestCase:
         # join 3 tables -- bug exists
         tdSql.error("select stb_t.ts, stb_t.dscrption, stb_t.temperature, stb_p.id, stb_p.dscrption, stb_p.pressure,stb_v.velocity from stb_p, stb_t, stb_v where stb_p.ts=stb_t.ts and stb_p.ts=stb_v.ts and stb_p.id = stb_t.id")
 
+        tdSql.error("select * from stb1 whern c1 > 'test' limit 100")
+
         # query show stable
         tdSql.query("show stables")
         tdSql.checkRows(1)

tests/pytest/query/queryNullValueTest.py

@@ -42,6 +42,9 @@ class TDTestCase:
         tdSql.prepare()
         
         for i in range(len(self.types)):
+            tdSql.execute("drop table if exists t0")
+            tdSql.execute("drop table if exists t1")
+            
             print("======== checking type %s ==========" % self.types[i])
             tdSql.execute("create table t0 (ts timestamp, col %s)" % self.types[i])
             tdSql.execute("insert into t0 values (%d, NULL)" % (self.ts))