So the issue caused by the optimization made by MDB. It removes intc b/c there is IN + single constant. If you run the query with at least two constants it works. If you switch the GROUP BY order it works b/c GROUP BY key is now 2 columns not one.

There is a fix ready for this issue.

Next release will both contain a workaround that enables SH for INSERT..SELECT and fix for Derived Handler.

4 QA: you should also test:

create table t2 as select * from (SELECT id,intc FROM C2 WHERE intc IN (201909) GROUP BY id,intc) as sel1;
select * into outfile '/tmp/result.dml' from (SELECT id,intc FROM C2 WHERE intc IN (201909) GROUP BY id,intc) as sel1;

Had been solved in the hotfix for 1.4.3.

The corner case(single top level subquery wrap) described by this issue fails in 1.4 and 1.5.
MDB doesn't find SH b/c SELECT_LEX::find_select_handler() gets only a subquery TABLE that can't ColumnStore handler.

I just retested it and it works in 5.5.2. There was an MDEV ticket which is responsible for fixing it - but of course I can't fine it (maybe drrtuy can recover it).

In either case, let's formally test it in 5.6.1 branch (5.5.2 is too late), so at lease we will be able to get it into the release notes and tell the world that it is fixed then.

Build tested: 5.6.1 (Drone #1915)

The issue reported in the bug description has been fixed, but another issue mentioned in the comment still exists.

MariaDB [mytest]> create table t2 as select * from (SELECT id,intc FROM C2 WHERE intc IN (201909) GROUP BY id,intc) as sel1;
Query OK, 0 rows affected (0.016 sec)
Records: 0 Duplicates: 0 Warnings: 0

MariaDB [mytest]> select * into outfile '/tmp/result.dml' from (SELECT id,intc FROM C2 WHERE intc IN (201909) GROUP BY id,intc) as sel1;
ERROR 1815 (HY000): Internal error: IDB-2021: 'intc' is not in GROUP BY clause. All non-aggregate columns in the SELECT and ORDER BY clause must be included in the GROUP BY clause.

The query would work without the outfile clause

MariaDB [mytest]> select * from (SELECT id,intc FROM C2 WHERE intc IN (201909) GROUP BY id,intc) as sel1;
Empty set (0.011 sec)

The original complaint has been corrected by MDEV-24298 and verified in 5.5.2 by GD and in develop by Daniel. New ticket - MCOL-4637 was created to deal with the ajacent problem (same error message this time on select into file)