TiDB push down NULL Set literal, while both TiFlash and TiKV not support it

[windtalker]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

create table t(a int ,b set("a"),c varchar(10));
alter table t set tiflash replica 1;

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

query return results.

3. What did you see instead (Required)

In TiDB + TiFlash

select * from t as x where x.c > (select b from t as y where y.a>1 limit 1); -- expect successfully; but got
-- ERROR 1105 (HY000): Illegal types of arguments (String, UInt64) of function greater

In TiDB + TiKV

mysql> select * from t as x where x.c > (select b from t as y where y.a>1 limit 1);select * from t as x where x.c > (select b from t as y where y.a>1 limit 1);
ERROR 1105 (HY000): other error: [components/tidb_query_expr/src/types/expr_builder.rs:295]: Invalid compare_bytes (sig = GtString) signature: Evaluate error: [components/tidb_query_expr/src/types/function.rs:268]: Unsupported type: Set

4. What is your TiDB version? (Required)

master @dbd31ad0441c4e0feba69773c6a7d21154a6ccef

[cosven]

/sig execution
/severity moderate