test: add test cases for timeline function used for select * union query

tests/system-test/2-query/union.py

@@ -231,6 +231,31 @@ class TDTestCase:
                     tdSql.execute(f"{sqls[j+i]} union {sqls[i]}")
                 else:
                     tdSql.error(f"{sqls[i]} union {sqls[j+i]}")
+        # check union with timeline function
+        tdSql.query(f"select first(c1) from (select * from t1 union select * from t1 order by ts)")
+        tdSql.checkRows(1)
+        tdSql.checkData(0, 0, 9)
+        tdSql.query(f"select last(c1) from (select * from t1 union select * from t1 order by ts desc)")
+        tdSql.checkRows(1)
+        tdSql.checkData(0, 0, 2147450880)
+        tdSql.query(f"select irate(c1) from (select * from t1 union select * from t1 order by ts)")
+        tdSql.checkRows(1)
+        tdSql.checkData(0, 0, 9.102222222222222)
+        tdSql.query(f"select elapsed(ts) from (select * from t1 union select * from t1 order by ts)")
+        tdSql.checkRows(1)
+        tdSql.checkData(0, 0, 46800000.000000000000000)
+        tdSql.query(f"select diff(c1) from (select * from t1 union select * from t1 order by ts)")
+        tdSql.checkRows(14)
+        tdSql.query(f"select derivative(c1, 1s, 0) from (select * from t1 union select * from t1 order by ts)")
+        tdSql.checkRows(11)
+
+        tdSql.error(f"select first(c1) from (select * from t1 union select * from t1)")
+        tdSql.error(f"select last(c1) from (select * from t1 union select * from t1)")
+        tdSql.error(f"select irate(c1) from (select * from t1 union select * from t1)")
+        tdSql.error(f"select elapsed(ts) from (select * from t1 union select * from t1)")
+        tdSql.error(f"select diff(c1) from (select * from t1 union select * from t1)")
+        tdSql.error(f"select derivative(c1, 1s, 0) from (select * from t1 union select * from t1)")
+
 
     def __test_error(self, dbname="db"):