sql-server - 如何让 SQL Server FOR XML 有效地格式化浮点数

Question

当我使用 FOR XMLfloat从我的 SQL 数据库中获取类型值时，它会将它们格式化为科学格式，如下所示：

<foo bar="0.00000000e+000"/>

我更喜欢它说“0”。

我怎样才能说服它这样做？

Answer 1

CAST是你的朋友

declare @t table (bar float);    insert @t values (0);
select bar from @t for xml path('foo');

------------------------------------------------
| <foo><bar>0.000000000000000e+000</bar></foo> |


declare @t table (bar float);    insert @t values (0);
select CAST(bar as decimal(10,2)) bar from @t for xml path('foo');

--------------------------------------------
|               <foo><bar>0.00</bar></foo> |


declare @t table (bar float);    insert @t values (0);
select CAST(bar as bigint) bar from @t for xml path('foo');

--------------------------------------------
|                  <foo><bar>0</bar></foo> |

Answer 2

CAST是你的敌人。它会显着降低性能。读这个。

Answer 3

使用我的功能，当需要兼容 Excel 或 SAS 等其他系统时使用 12 位精度，NB！它也有 ROUND

CREATE OR ALTER FUNCTION dbo.FormatAbacus( @p FLOAT(53)) 
RETURNS VARCHAR(40) 
AS 
BEGIN 
   DECLARE @dec INT = 10 -- may be as parameter in future
   DECLARE @SIGN  AS CHAR(1) = IIF( @p < 0 , '-', NULL);
   IF @p IS NULL RETURN NULL
   IF @p = 0 RETURN '0'
   SET @p = ABS( @p);
   DECLARE @exp      AS INT         = FLOOR(LOG10(@p)) ;
   DECLARE @power    AS FLOAT       = POWER( CONVERT(FLOAT,10.0), @dec - @exp - 1);
   DECLARE @mantis   AS VARCHAR(40) = CONVERT( NUMERIC, ROUND( @p * @power,0));
   DECLARE @ret      AS VARCHAR(40) = CASE
            WHEN 0 > @exp THEN CONCAT( LEFT( '0.00000000000000',1-@exp), @mantis)
            WHEN @exp >= @dec THEN CONCAT( @mantis,LEFT( '000000000000000',@exp-@dec+1))
            WHEN @exp = @dec - 1 THEN @mantis
            ELSE STUFF( @mantis, @exp+2, 0, '.')
         END;
   IF @ret LIKE '%.%' SET @ret = LEFT( @ret, LEN(RTRIM(REPLACE(@ret,'0',' '))))
   IF @ret LIKE '%.' SET @ret = REPLACE(@ret,'.','')
   RETURN CONCAT( @SIGN, @ret)
END

跑：

SELECT 
      dbo.FormatAbacus(0.001234567890123456)              AS '_0.001234567890123456'
   ,  dbo.FormatAbacus(  0.1234567890123456)              AS '_0.1234567890123456'  
   ,  dbo.FormatAbacus(   1.234567890123456)              AS '_1.234567890123456'   
   ,  dbo.FormatAbacus(   123456.7890123456)              AS '_123456.7890123456'   
   ,  dbo.FormatAbacus(   123456789012.3456)              AS '_123456789012.3456'   
   ,  dbo.FormatAbacus(   12345678901234.56)              AS '_12345678901234.56'   
   ,  dbo.FormatAbacus(   12345678901234560.)             AS '_12345678901234560.'  
   ,  dbo.FormatAbacus(   123456789012345600.)            AS '_123456789012345600.' 
   ,  dbo.FormatAbacus(NULL)                              AS '_NULL'                
   ,  dbo.FormatAbacus(0)                                 AS '_0'                
FOR XML PATH('Abacus_12_digits'),TYPE 

产品：

<Abacus_12_digits>
  <_0.001234567890123456>0.00123456789012     </_0.001234567890123456>
  <_0.1234567890123456>    0.123456789012     </_0.1234567890123456>
  <_1.234567890123456>      1.23456789012     </_1.234567890123456>
  <_123456.7890123456>      123456.789012     </_123456.7890123456>
  <_123456789012.3456>      123456789012      </_123456789012.3456>
  <_12345678901234.56>      12345678901200    </_12345678901234.56>
  <_12345678901234560.>     12345678901200000 </_12345678901234560.>
  <_123456789012345600.>    123456789012000000</_123456789012345600.>
  <!--                      NULL is missing    -->
  <_0>                      0                 </_0>
</Abacus_12_digits>