Got error when substring is used in filter

[guo-shaoge]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

drop table t1;
create table t1(c1 varchar(100), c2 varchar(100), key(c1), key(c2), c3 varchar(100));
insert into t1 values('ab', '10', '10');
explain select /*+ use_index_merge(t1) */ * from t1 where c1 = 'ab' or c2 = '10' and substring(c3, 10) = 10;
select /*+ use_index_merge(t1) */ * from t1 where c1 = 'ab' or c2 = '10' and substring(c3, 10) = 10;

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

no error

3. What did you see instead (Required)

other error: [components/tidb_query_expr/src/lib.rs:705]: ScalarFunction Substring2ArgsUtf8 is not supported in batch mode

4. What is your TiDB version? (Required)

master

[guo-shaoge]

There are two ways to fix this:

1. The simpler one: pushdown substring and char_length, just as expression: enable pushdown substring/char_length to tikv #30193 did.
2. More thorough repair: fix the plan, add Selection above IndexMerge if some exprs cannot be pushdown, just as planner: fix index merge plan when expr cannot be pushed to tikv #30341 did.

[github-actions]

Please check whether the issue should be labeled with 'affects-x.y' or 'fixes-x.y.z', and then remove 'needs-more-info' label.