diff --git a/tests/pytest/functions/function_first.py b/tests/pytest/functions/function_first.py
index 6c3a747febae03ab90ef8275abbf84283cc07d95..df9056acfe8fc5d3617511c3cdb12470903fa71b 100644
--- a/tests/pytest/functions/function_first.py
+++ b/tests/pytest/functions/function_first.py
@@ -162,7 +162,7 @@ class TDTestCase:
         text = r.read()
         r.close()
         result = float(re.split('\n |\|', text)[3])
-        tdSql.query("select first(c1) + last(c1) from tb01")
+        tdSql.query("select first(c1) - last(c1) from tb01")
         tdSql.checkData(0, 0, result)