create table ten(a int);
insert into ten values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
create table t10 (
  a int not null
) partition by key(a);
insert into t10 select a from ten;
explain partitions select * from t10 where a in (2,3,4);

MariaDB [j2]> explain partitions select * from t10 where a in (2,3,4);
+------+-------------+-------+------------+------+---------------+------+---------+------+------+-------------+
| id   | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | Extra       |
+------+-------------+-------+------------+------+---------------+------+---------+------+------+-------------+
|    1 | SIMPLE      | t10   | p0         | ALL  | NULL          | NULL | NULL    | NULL |   10 | Using where |
+------+-------------+-------+------------+------+---------------+------+---------+------+------+-------------+

MariaDB [j2]> explain format=json select * from t10 where a in (2,3,4)\G
*************************** 1. row ***************************
EXPLAIN: {
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t10",
      "access_type": "ALL",
      "rows": 10,
      "filtered": 100,
      "attached_condition": "(t10.a in (2,3,4))"
    }
  }
}

MySQL [test]> explain format=json select * from t10 where a in (2,3,4)\G
*************************** 1. row ***************************
EXPLAIN: {
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "t10",
      "partitions": [
        "p0"
      ],
      "access_type": "ALL",
      "rows": 10,
      "filtered": 100,
      "attached_condition": "(`test`.`t10`.`a` in (2,3,4))"
    }
  }
}