VARCHAR 详解[通俗易懂]

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发布于 2022-09-19 22:26:45

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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(20));
Query OK, 0 rows affected (0.27 sec)

mysql> show create table t1;
+-------+---------------------------------------------------------------
| Table | Create Table
+-------+---------------------------------------------------------------
| t1    | CREATE TABLE `t1` (
  `a` varchar(20) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+---------------------------------------------------------------
1 row in set (0.00 sec)

mysql> insert into t1 select repeat("a",21);
ERROR 1406 (22001): Data too long for column 'a' at row 1

mysql> insert into t1 select repeat("a",20);
Query OK, 1 row affected (0.09 sec)
Records: 1 Duplicates: 0 Warnings: 0

mysql> insert into t1 select repeat("我",21);
ERROR 1406 (22001): Data too long for column 'a' at row 1

mysql> insert into t1 select repeat("我",20);
Query OK, 1 row affected (0.11 sec)
Records: 1 Duplicates: 0 Warnings: 0

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, 1 row affected (0.09 sec)
Records: 1 Duplicates: 0 Warnings: 0

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 1406 (22001): Data too long for column 'a' at row 1

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(21844) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+-------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)

mysql> create table a( a varchar(65535));
ERROR 1074 (42000): Column length too big for column 'a' (max = 21845); use BLOB or TEXT instead

mysql> create table a( a varchar(65532));
ERROR 1074 (42000): Column length too big for column 'a' (max = 21845); use BLOB or TEXT instead

mysql> create table a( a varchar(21845));
ERROR 1118 (42000): Row size too large. The maximum row size for the used table type, not counting BLOBs, is 65535. This includes st
eck the manual. You have to change some columns to TEXT or BLOBs

mysql> create table a( a varchar(21844));
Query OK, 0 rows affected (0.31 sec)

表为latin1字符集:

mysql> create table a1 ( a varchar(65535))charset=latin1;
ERROR 1118 (42000): 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(65534))charset=latin1;
ERROR 1118 (42000): 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(65533))charset=latin1;
ERROR 1118 (42000): 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(65532))charset=latin1;
Query OK, 0 rows affected (0.33 sec)

不能插入汉字：

mysql> insert into a1 select repeat("我",65532);
ERROR 1366 (HY000): Incorrect string value: '\xE6\x88\x91\xE6\x88\x91...' for column 'a' at row 1
mysql> insert into a1 select "我";
ERROR 1366 (HY000): Incorrect string value: '\xE6\x88\x91' for column 'a' at row 1


mysql> insert into a1 select repeat("a",65532);
Query OK, 1 row affected (0.17 sec)
Records: 1  Duplicates: 0  Warnings: 0

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