mysql - MySQL中VARCHAR(255)的存储大小是多少

Question

我能够在数据类型为 VARCHAR(255) 的 MySQL 列中存储超过 255 个字符(例如“a”)。请澄清

Answer 1

字符列的最大存储大小由宽度定义(即 255)。您可以插入较短的值，但它们将被截断并显示警告。

如果您使用其中一种严格的 SQL 模式，它将产生错误而不是警告。

查看文档: https://dev.mysql.com/doc/refman/5.6/en/string-type-overview.html

mysql [localhost] {msandbox} (test) > CREATE TABLE t_varchar(a VARCHAR(127));
Query OK, 0 rows affected (0.02 sec)

mysql [localhost] {msandbox} (test) > SET sql_mode='';
Query OK, 0 rows affected (0.00 sec)

mysql [localhost] {msandbox} (test) > INSERT INTO t_varchar VALUES(REPEAT('a', 127));
Query OK, 1 row affected (0.00 sec)

mysql [localhost] {msandbox} (test) > INSERT INTO t_varchar VALUES(REPEAT('a', 128));
Query OK, 1 row affected, 1 warning (0.00 sec)

mysql [localhost] {msandbox} (test) > SELECT LENGTH(a) FROM t_varchar;
+-----------+
| LENGTH(a) |
+-----------+
|       127 |
|       127 |
+-----------+
2 rows in set (0.00 sec)

mysql [localhost] {msandbox} (test) > 
mysql [localhost] {msandbox} (test) > TRUNCATE TABLE t_varchar;
Query OK, 0 rows affected (0.00 sec)

mysql [localhost] {msandbox} (test) > SET sql_mode='STRICT_ALL_TABLES';
Query OK, 0 rows affected (0.00 sec)

mysql [localhost] {msandbox} (test) > INSERT INTO t_varchar VALUES(REPEAT('a', 127));
Query OK, 1 row affected (0.00 sec)

mysql [localhost] {msandbox} (test) > INSERT INTO t_varchar VALUES(REPEAT('a', 128));
ERROR 1406 (22001): Data too long for column 'a' at row 1
mysql [localhost] {msandbox} (test) > SELECT LENGTH(a) FROM t_varchar;
+-----------+
| LENGTH(a) |
+-----------+
|       127 |
+-----------+
1 row in set (0.00 sec)