Mysql实例mysql字符与数字转换

发布时间：2020-12-12 02:30:13 所属栏目：MySql教程来源：网络整理

导读：《Mysql实例mysql字符与数字转换》要点：本文介绍了Mysql实例mysql字符与数字转换，希望对您有用。如果有疑问，可以联系我们。导读：本节内容：mysql字符与数字转换的办法1,将字符的数字转成数字,比如0转成0可以直接用加法实现.例如：将pony表中的d 进行排

《Mysql实例mysql字符与数字转换》要点：
本文介绍了Mysql实例mysql字符与数字转换，希望对您有用。如果有疑问，可以联系我们。

导读：本节内容：mysql字符与数字转换的办法1,将字符的数字转成数字,比如0转成0可以直接用加法实现.例如：将pony表中的d 进行排序,可d的定义...

MYSQL实例?本节内容：
mysql字符与数字转换的办法

MYSQL实例1,比如'0'转成0可以直接用加法实现.

MYSQL实例例如：将pony表中的d 进行排序,可d的定义为varchar：
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select * from pony order by (d+0)

MYSQL实例2,在进行ifnull处理时,比如 ifnull(a/b,'0') 会导致 a/b成了字符串,因此需要把'0'改成0.

MYSQL实例3,比较数字和varchar时,比如a=11,b="11ddddd";

MYSQL实例则 select 11="11ddddd"相等

MYSQL实例绝对比较可以这样：
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select binary 11 =binary "11ddddd"
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MYSQL实例?
附1,
字符集转换 :?? CONVERT(xxx? USING?? gb2312)
类型转换和SQL Server一样,就是类型参数有点点不同? : CAST(xxx? AS?? 类型)?,?? CONVERT(xxx,类型),类型必须用下列的类型：
1,可用的类型　??
2,二进制,同带binary前缀的效果 : BINARY???
3,字符型,可带参数 : CHAR()????
4,日期 : DATE????
5,时间: TIME????
6,日期时间型 : DATETIME????
7,浮点数 : DECIMAL?????
8,整数 : SIGNED????
9,无符号整数 : UNSIGNED
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附2,
To cast a string to a numeric value in numeric context,you normally do not have to do anything other than to use the string value as though it were a number:
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mysql> SELECT 1+'1';
-> 2

MYSQL实例If you use a number in string context,the number automatically is converted to a BINARY string.
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mysql> SELECT CONCAT('hello you ',2);
-> 'hello you 2'

MYSQL实例MySQL supports arithmetic with both signed and unsigned 64-bit values. If you are using numeric operators (such as + or -) and one of the operands is an unsigned integer,the result is unsigned. You can override this by using the SIGNED and UNSIGNED cast operators to cast the operation to a signed or unsigned 64-bit integer,respectively.
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MYSQL实例mysql> SELECT CAST(1-2 AS UNSIGNED)
-> 18446744073709551615

MYSQL实例mysql> SELECT CAST(CAST(1-2 AS UNSIGNED) AS SIGNED);
-> -1

MYSQL实例Note that if either operand is a floating-point value,the result is a floating-point value and is not affected by the preceding rule. (In this context,DECIMAL column values are regarded as floating-point values.)
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mysql> SELECT CAST(1 AS UNSIGNED) - 2.0;
-> -1.0

MYSQL实例If you are using a string in an arithmetic operation,this is converted to a floating-point number.

MYSQL实例If you convert a “zero” date string to a date,CONVERT() and CAST() return NULL when the NO_ZERO_DATE SQL mode is enabled. As of MySQL 5.0.4,they also produce a warning.

MYSQL实例有关MYSQL字符与数字转换的办法,就介绍这些吧,希望对大家有所帮助.

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