Get different result from MySQL when using multi-valued index

[xiongjiwei]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

-- 1
set names gbk;
create table t(a json, b int, index idx3(b, (cast(a as char(10) array))));

-- 2
create table t1(pk int primary key, a json, index idx((cast(a as signed array))));
insert into t1 values (6, '1');

-- 3
create table t(a json, index idx(((cast(a as signed array)))));
insert into t1 values (6, '1');
select * from t1 where 1 member of (a);

2. What did you expect to see? (Required)

3. What did you see instead (Required)

4. What is your TiDB version? (Required)