support push calculation of type 'enum' to TiFlash

[giant-panda666]

Feature Request

Is your feature request related to a problem? Please describe:

1. create table t0 and t1

   create table t0(id int primary key, v int, vv enum('A1', 'A2', 'A3'));
   create table t1(id int primary key, v int, vv enum('B1', 'B2', 'B3'));

2. execute expain

   explain analyze select/*+ read_from_storage(tiflash[a], tiflash[b]) */ a.v, b.v, a.vv, b.vv from t0 a join t1 b on a.id=b.id where a.vv='A1';

   

there are some warnings:

enum type is used frequently as basic type, so why TiFlash don't support it ?

Describe the feature you'd like:

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy: