mysql READ-COMMITTED 模式下 行锁不会升级到表级锁

mysql> select sn,id,info from s100 group by id;
+-----+------+------+
| sn  | id   | info |
+-----+------+------+
| 227 |    1 | aa   |
| 228 |    2 | bb   |
+-----+------+------+
2 rows in set (0.02 sec)

mysql> select sn,count(id),info from s100 group by id;
+-----+-----------+------+
| sn  | count(id) | info |
+-----+-----------+------+
| 227 |     32768 | aa   |
| 228 |         1 | bb   |
+-----+-----------+------+
2 rows in set (0.02 sec)

mysql>
mysql>
mysql> show index from s100;
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| s100  |          0 | PRIMARY  |            1 | sn          | A         |       33366 |     NULL | NULL   |      | BTREE      |         |               |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
1 row in set (0.00 sec)

mysql>  show variables like '%tx_isolation%';
+---------------+----------------+
| Variable_name | Value          |
+---------------+----------------+
| tx_isolation  | READ-COMMITTED |
+---------------+----------------+
1 row in set (0.00 sec)

mysql> show variables like '%commit%';
+--------------------------------+-------+
| Variable_name                  | Value |
+--------------------------------+-------+
| autocommit                     | OFF   |
| binlog_order_commits           | ON    |
| innodb_api_bk_commit_interval  | 5     |
| innodb_commit_concurrency      | 0     |
| innodb_flush_log_at_trx_commit | 1     |
+--------------------------------+-------+
5 rows in set (0.00 sec)

Session 1:

mysql> select * from s100 where id=2 for update;
+-----+------+------+
| sn  | id   | info |
+-----+------+------+
| 228 |    2 | bb   |
+-----+------+------+
1 row in set (0.02 sec)

Session 2:

Database changed
mysql> insert into s100(id,info) values(9999,'fcadfad');
Query OK, 1 row affected (0.00 sec)

RC模式下,是行锁 不会上升到表级锁