《Mysql實例mysql字符與數(shù)字轉(zhuǎn)換》要點：
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MYSQL實例?本節(jié)內(nèi)容：
mysql字符與數(shù)字轉(zhuǎn)換的辦法
MYSQL實例1,將字符的數(shù)字轉(zhuǎn)成數(shù)字,比如'0'轉(zhuǎn)成0可以直接用加法實現(xiàn).
MYSQL實例例如：將pony表中的d 進行排序,可d的定義為varchar：
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MYSQL實例2,在進行ifnull處理時,比如 ifnull(a/b,'0') 會導(dǎo)致 a/b成了字符串,因此需要把'0'改成0.
MYSQL實例3,比較數(shù)字和varchar時,比如a=11,b="11ddddd";
MYSQL實例則 select 11="11ddddd"相等
MYSQL實例絕對比較可以這樣：
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MYSQL實例?
附1,
字符集轉(zhuǎn)換 :?? CONVERT(xxx? USING?? gb2312)
類型轉(zhuǎn)換和SQL Server一樣,就是類型參數(shù)有點點不同? : CAST(xxx? AS?? 類型)? ,?? CONVERT(xxx,類型),類型必須用下列的類型：
1,可用的類型 ??
2,二進制,同帶binary前綴的效果 : BINARY???
3,字符型,可帶參數(shù) : CHAR()????
4,日期 : DATE????
5,時間: TIME????
6,日期時間型 : DATETIME????
7,浮點數(shù) : DECIMAL?????
8,整數(shù) : SIGNED????
9,無符號整數(shù) : 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實例If you use a number in string context, the number automatically is converted to a BINARY string.
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MYSQL實例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實例mysql> SELECT CAST(1-2 AS UNSIGNED)
-> 18446744073709551615
MYSQL實例mysql> SELECT CAST(CAST(1-2 AS UNSIGNED) AS SIGNED);
-> -1
MYSQL實例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實例If you are using a string in an arithmetic operation, this is converted to a floating-point number.
MYSQL實例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實例有關(guān)MYSQL字符與數(shù)字轉(zhuǎn)換的辦法,就介紹這些吧,希望對大家有所幫助.
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