bug: incorrect result set.After update trigger,Does not take effect

[shangyanwen]

Describe the problem

create table t1 (i int)engine=tianmu;
insert into t1 values (1),(2),(3),(4);
create trigger trg after update on t1 for each row
  set @total_change:=@total_change + new.i - old.i;
set @total_change:=0;
update t1 set i=3;
select @total_change;

#Incorrect test results
+---------------+
| @total_change |
+---------------+
|             0 |
+---------------+
1 row in set (0.00 sec)

drop trigger trg;
drop table t1;

Expected behavior

# Correct test results（note:Innodb test verification, test results are as follows）
mysql> select @total_change;
+---------------+
| @total_change |
+---------------+
|             2 |
+---------------+

How To Reproduce

Follow the test steps above

Environment

./mysqld  Ver 5.7.36_v1.0.1_beta-StoneDB for Linux on x86_64 (build-)
build information as follow: 
        Repository address: https://github.com/stoneatom/stonedb.git:stonedb-5.7-dev
        Branch name: stonedb-5.7-dev
        Last commit ID: 208f79d
        Last commit time: Date:   Sat Sep 17 16:19:42 2022 +0800
        Build time: Date: Sat Sep 17 17:59:04 CST 2022

Are you interested in submitting a PR to solve the problem?

• Yes, I will!

[lylth]

This bug has been fixed

mysql> create table t1 (i int)engine=tianmu;
Query OK, 0 rows affected (0.00 sec)

mysql> insert into t1 values (1),(2),(3),(4);
Query OK, 4 rows affected (0.00 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> create trigger trg after update on t1 for each row
    ->   set @total_change:=@total_change + new.i - old.i;
Query OK, 0 rows affected (0.01 sec)

mysql> set @total_change:=0;
Query OK, 0 rows affected (0.00 sec)

mysql> update t1 set i=3;
Query OK, 3 rows affected (0.01 sec)
Rows matched: 4  Changed: 3  Warnings: 0

mysql> select @total_change;
+---------------+
| @total_change |
+---------------+
|             2 |
+---------------+
1 row in set (0.00 sec)