plan cache: expression.Expression is *expression.Constant, not *expression.Column

[ChenPeng2013]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

prepared-plan-cache.enabled=true

use test;
drop table if exists t;
create table t(a int);
prepare stmt from "select * from t order by rand()";
execute stmt;

2. What did you expect to see?

mysql> execute stmt;
Empty set (0.01 sec)

3. What did you see instead?

mysql> execute stmt;
ERROR 1105 (HY000): interface conversion: expression.Expression is *expression.Constant, not *expression.Column

4. What version of TiDB are you using? (tidb-server -V or run select tidb_version(); on TiDB)

Release Version: v4.0.0-beta.2-151-g78922a8ab
Git Commit Hash: 78922a8abef2f21e4d8990d37c6c67ac7b0eef42
Git Branch: release-4.0
UTC Build Time: 2020-04-07 06:22:22
GoVersion: go1.13.1
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false