参数TINYINT(parameter)的含义是什么? [英] What is the meaning parameter TINYINT(parameter)?

问题描述

我不明白为什么选择这个选项. 带符号的TINYINT数据类型可以存储-128到127之间的整数值.

I can not understand why this option. The signed TINYINT data type can store integer values between -128 and 127.

mysql> create table b (i tinyint(1));

mysql> insert into b values (42);

mysql> select * from b;
+------+
| i    |
+------+
|   42 |
+------+

推荐答案

数据方面的tinyint(1)，tinyint(2)，tinyint(3)等完全相同.对于SIGNED，它们都在-128到127之间；对于UNSIGNED，它们都在0-255之间.正如其他答案所指出的那样，括号中的数字仅是显示宽度的提示.

Data-wise, tinyint(1), tinyint(2), tinyint(3) etc. are all exactly the same. They are all in the range -128 to 127 for SIGNED or 0-255 for UNSIGNED. As other answers noted the number in parenthesis is merely a display width hint.

不过，您可能要注意，应用程序=明智的事物看起来可能有所不同.在这里，tinyint(1)可能具有特殊含义.例如，Connector/J(Java连接器)将tinyint(1)视为布尔值，并且不将数值结果返回给应用程序，而是将值转换为true和false.可以通过tinyInt1isBit=false连接参数进行更改.

You might want to note, though, that application=wise things may look different. Here, tinyint(1) can take a special meaning. For example, the Connector/J (Java connector) treats tinyint(1) as a boolean value, and instead of returning a numerical result to the application, it converts values to true and false. this can be changed via the tinyInt1isBit=false connection parameter.

由于数据类型为8位(1字节)，tinyint(1)可以容纳-128到127之间的数字-显然，无符号的tinyint可以容纳值0-255.

A tinyint(1) can hold numbers in the range -128 to 127, due to the datatype being 8 bits (1 byte) - obviously an unsigned tinyint can hold values 0-255.

它会自动截断超出范围的值:

It will silently truncate out of range values:

mysql> create table a
    -> (
    ->    ttt tinyint(1)
    -> );
Query OK, 0 rows affected (0.01 sec)

mysql> insert into a values ( 127 );
Query OK, 1 row affected (0.00 sec)

mysql> insert into a values ( -128 );
Query OK, 1 row affected (0.00 sec)

mysql> insert into a values ( 128 );
Query OK, 1 row affected, 1 warning (0.00 sec)

mysql> insert into a values ( -129 );
Query OK, 1 row affected, 1 warning (0.00 sec)

mysql> select * from a;
+------+
| ttt  |
+------+
|  127 |
| -128 |
|  127 |
| -128 |
+------+
4 rows in set (0.00 sec)

mysql>

...，除非您更改sql_mode或更改服务器配置:

... unless you change the sql_mode or change the server config:

mysql> set sql_mode=STRICT_ALL_TABLES;
Query OK, 0 rows affected (0.00 sec)

mysql> insert into a values ( -129 );
ERROR 1264 (22003): Out of range value for column 'ttt' at row 1
mysql>

在DDL中用于数据类型的值(例如:tinyint(1))，正如您所怀疑的那样，是显示宽度.但是，它是可选的，客户端不必使用它.例如，标准的MySQL客户端不使用它.

The value used in the DDL for the datatype (eg: tinyint(1)) is, as you suspected, the display width. However, it is optional and clients don't have to use it. The standard MySQL client doesn't use it, for example.

https://dev .mysql.com/doc/refman/5.1/en/integer-types.html

https://dev.mysql.com/doc/refman/5.0/en/numeric-type-overview.html

MySql:Tinyint(2)vs tinyint( 1)-有什么区别?

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