VARCHAR 详解

varchar(20):20指的是表中的a字段能存储的最大字符个数

In contrast to CHAR, VARCHAR values are stored as a 1-byte or 2-byte length prefix plus data.

The length prefix indicates the number of bytes in the value.

A column uses one length byte if values require no more than 255 bytes,

two length bytes if values may require more than 255 bytes.

mysql> create table t1( a varchar());
Query OK,  rows affected (0.27 sec)

mysql> show create table t1;
+-------+---------------------------------------------------------------
| Table | Create Table
+-------+---------------------------------------------------------------
| t1    | CREATE TABLE `t1` (
  `a` varchar() DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+---------------------------------------------------------------
 row in set (0.00 sec)

mysql> insert into t1 select repeat("a",);
ERROR  (): Data too long for column 'a' at row 

mysql> insert into t1 select repeat("a",);
Query OK,  row affected (0.09 sec)
Records:  Duplicates:  Warnings: 

mysql> insert into t1 select repeat("我",);
ERROR  (): Data too long for column 'a' at row 

mysql> insert into t1 select repeat("我",);
Query OK,  row affected (0.11 sec)
Records:  Duplicates:  Warnings: 

mysql> insert into t1 select "我我我我我我我我我我我我我我我我我我我1";
Query OK,  row affected (0.09 sec)
Records:  Duplicates:  Warnings: 

mysql> insert into t1 select "我我我我我我我我我我我我我我我我我我我11";
ERROR  (): Data too long for column 'a' at row 

varchar 存储极限:

表为utf8字符集:

mysql> show create table a;
+-------+-------------------------------------------------------------------------------------------+
| Table | Create Table                                                                              |
+-------+-------------------------------------------------------------------------------------------+
| a     | CREATE TABLE `a` (
  `a` varchar() DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+-------------------------------------------------------------------------------------------+
 row in set (0.01 sec)

mysql> create table a( a varchar());
ERROR  (): Column length too big for column 'a' (max = ); use BLOB or TEXT instead
mysql> create table a( a varchar());
ERROR  (): Column length too big for column 'a' (max = ); use BLOB or TEXT instead
mysql> create table a( a varchar());
ERROR  (): Row size too large. The maximum row size for the used table type, not counting BLOBs, is . This includes st
eck the manual. You have to change some columns to TEXT or BLOBs
mysql> create table a( a varchar());
Query OK,  rows affected (0.31 sec)

表为latin1字符集:

mysql> create table a1 ( a varchar())charset=latin1;
ERROR  (): Row size too large. The maximum row size for the used table type, not counting BLOBs,
eck the manual. You have to change some columns to TEXT or BLOBs
mysql> create table a1 ( a varchar())charset=latin1;
ERROR  (): Row size too large. The maximum row size for the used table type, not counting BLOBs,
eck the manual. You have to change some columns to TEXT or BLOBs
mysql> create table a1 ( a varchar())charset=latin1;
ERROR  (): Row size too large. The maximum row size for the used table type, not counting BLOBs,
eck the manual. You have to change some columns to TEXT or BLOBs
mysql> create table a1 ( a varchar())charset=latin1;
Query OK,  rows affected (0.33 sec)

不能插入汉字：

mysql> insert into a1 select repeat("我",);
ERROR  (HY000): Incorrect string value: '\xE6\x88\x91\xE6\x88\x91...' for column 'a' at row
mysql> insert into a1 select "我";
ERROR  (HY000): Incorrect string value: '\xE6\x88\x91' for column 'a' at row 1

mysql> insert into a1 select repeat("a",);
Query OK,  row affected (0.17 sec)
Records:   Duplicates:   Warnings: