要想计算用于保存具体CHAR、VARCHAR或者TEXT列值的字节数，需要考虑该列使用的字符集。在具体情况中，当使用Unicode时，必须记住所有Unicode字符使用相同的字节数。
mysql> show variables like '%char%';
+--------------------------+-------------------------------------------+
| Variable_name | Value |
+--------------------------+-------------------------------------------+
| character_set_client | gbk |
| character_set_connection | gbk |
| character_set_database | gbk |
| character_set_results | gbk |
| character_set_server | gbk |
| character_set_system | utf8 |
| character_sets_dir | d:\mysql-5.0.9-beta-win32\share\charsets/ |
+--------------------------+-------------------------------------------+
7 rows in set (0.00 sec)
mysql> create table t1(id char(4));
Query OK, 0 rows affected (0.13 sec)
mysql> insert into t1 values('中国');
Query OK, 1 row affected (0.05 sec)
mysql> select * from t1;
+------+
| id |
+------+
| 中国 |
+------+
1 row in set (0.00 sec)
mysql> insert into t1 values('中国强大');
Query OK, 1 row affected (0.06 sec)
mysql> select * from t1;
+----------+
| id |
+----------+
| 中国 |
| 中国强大 |
+----------+
2 rows in set (0.00 sec)
mysql> insert into t1 values('中国强大吗');
Query OK, 1 row affected, 1 warning (0.06 sec)
mysql> select * from t1;
+----------+
| id |
+----------+
| 中国 |
| 中国强大 |
| 中国强大 |
+----------+
3 rows in set (0.00 sec)
上边的实验也印证了char(4)在gbk字符集下最长可以存储4个汉字。
