《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。
MYSQL实例 本节内容：
mysql字符与数字转换的办法
MYSQL实例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.
MYSQL实例例如：将pony表中的d 进行排序,可d的定义为varchar：
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：
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
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:
MYSQL实例If you use a number in string context, the number automatically is converted to a BINARY string.
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.
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.)
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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