我正在使用 SQL Server 2008 R2 并且有一VARCHAR列我想转换为DECIMAL(28,10)使用CONVERT. 但是其中许多行格式错误，因此无法将它们解析为数字。在这种情况下，我只想通过将结果设置为 0 或 NULL 来跳过这些。
我知道 SQL Server 2012 ( ) 中有一条新语句TRY_CONVERT()会很方便。
这在 2008 年是否可行，或者我必须等到我们更新到下一个 SQL 2012 版本吗？
编辑
不幸ISNUMERIC()的是，在这种情况下不可靠。我试过
ISNUMERIC(myCol) = 1
对于CONVERT无法转换为DECIMAL.
在 SQL Server 中使用 XML 时，您可以尝试转换为数据类型并在转换失败时接收空值。
declare @T table
(
Col varchar(50)
)
insert into @T values
('1'),
('1.1'),
('1,1'),
('1a')
select cast('' as xml).value('sql:column("Col") cast as xs:decimal ?',
'decimal(28,10)') as Col
from @T
结果：
Col
-------------
1.0000000000
1.1000000000
NULL
NULL
由于这是一项永久性更改，因此我将分两步进行 - 首先，删除无效文本，然后转换列。
要删除无效文本，我会执行以下操作：
UPDATE [Table]
SET [Column] = NULL
WHERE [Column] LIKE '%[^0-9.]%' or
LEN([Column]) - LEN(REPLACE([Column],'.','')) > 1 or
LEN([Column]) > 28
完成后，剩下的所有东西都应该可以通过更改列定义来转换
ALTER TABLE [Table] ALTER COLUMN [Column] decimal(28,10)
您可以在 C# 中编写自己的自定义解析器并使用 SQLCLR，例如使用Decimal.Parse(). 不要尝试使用, 是出了名的不正确（对于 CAST 失败的字符串返回 TRUE）。ISNUMERIC
我写了一个有用的标量函数来模拟 SQL Server 2008 中 SQL SERVER 2012 的 TRY_CAST 函数。
dbo.TRY_CAST(Expression, Data_Type, ReturnValueIfErrorCast)
SQL Server 2012 的 TRY_CAST 函数的两个主要区别是您必须传递 3 个参数，并且您必须另外对字段执行显式 CONVERT 或 CAST。但是，它仍然非常有用，因为它允许您在未正确执行 CAST 时返回默认值。
功能代码：
DECLARE @strSQL NVARCHAR(1000)
IF NOT EXISTS (SELECT * FROM dbo.sysobjects WHERE id = OBJECT_ID(N'[dbo].[TRY_CAST]'))
BEGIN
SET @strSQL = 'CREATE FUNCTION [dbo].[TRY_CAST] () RETURNS INT AS BEGIN RETURN 0 END'
EXEC sys.sp_executesql @strSQL
END
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
/*
------------------------------------------------------------------------------------------------------------------------
Description:
Syntax
---------------
dbo.TRY_CAST(Expression, Data_Type, ReturnValueIfErrorCast)
+---------------------------+-----------------------+
| Expression | VARCHAR(8000) |
+---------------------------+-----------------------+
| Data_Type | VARCHAR(8000) |
+---------------------------+-----------------------+
| ReturnValueIfErrorCast | SQL_VARIANT = NULL |
+---------------------------+-----------------------+
Arguments
---------------
expression
The value to be cast. Any valid expression.
Data_Type
The data type into which to cast expression.
ReturnValueIfErrorCast
Value returned if cast fails or is not supported. Required. Set the DEFAULT value by default.
Return Type
----------------
Returns value cast to SQL_VARIANT type if the cast succeeds; otherwise, returns null if the parameter @pReturnValueIfErrorCast is set to DEFAULT,
or that the user indicates.
Remarks
----------------
dbo.TRY_CAST function simulates the TRY_CAST function reserved of SQL SERVER 2012 for using in SQL SERVER 2008.
dbo.TRY_CAST function takes the value passed to it and tries to convert it to the specified Data_Type.
If the cast succeeds, dbo.TRY_CAST returns the value as SQL_VARIANT type; if the cast doesn´t succees, null is returned if the parameter @pReturnValueIfErrorCast is set to DEFAULT.
If the Data_Type is unsupported will return @pReturnValueIfErrorCast.
dbo.TRY_CAST function requires user make an explicit CAST or CONVERT in ANY statements.
This version of dbo.TRY_CAST only supports CAST for INT, DATE, NUMERIC and BIT types.
Examples
====================================================================================================
--A. Test TRY_CAST function returns null
SELECT
CASE WHEN dbo.TRY_CAST('6666666166666212', 'INT', DEFAULT) IS NULL
THEN 'Cast failed'
ELSE 'Cast succeeded'
END AS Result;
GO
--B. Error Cast With User Value
SELECT
dbo.TRY_CAST('2147483648', 'INT', DEFAULT) AS [Error Cast With DEFAULT],
dbo.TRY_CAST('2147483648', 'INT', -1) AS [Error Cast With User Value],
dbo.TRY_CAST('2147483648', 'INT', NULL) AS [Error Cast With User NULL Value];
GO
--C. Additional CAST or CONVERT required in any assignment statement
DECLARE @IntegerVariable AS INT
SET @IntegerVariable = CAST(dbo.TRY_CAST(123, 'INT', DEFAULT) AS INT)
SELECT @IntegerVariable
GO
IF OBJECT_ID('tempdb..#temp') IS NOT NULL
DROP TABLE #temp
CREATE TABLE #temp (
Id INT IDENTITY
, FieldNumeric NUMERIC(3, 1)
)
INSERT INTO dbo.#temp (FieldNumeric)
SELECT CAST(dbo.TRY_CAST(12.3, 'NUMERIC(3,1)', 0) AS NUMERIC(3, 1));--Need explicit CAST on INSERT statements
SELECT *
FROM #temp
DROP TABLE #temp
GO
--D. Supports CAST for INT, DATE, NUMERIC and BIT types.
SELECT dbo.TRY_CAST(2147483648, 'INT', 0) AS [Cast failed]
, dbo.TRY_CAST(2147483647, 'INT', 0) AS [Cast succeeded]
, SQL_VARIANT_PROPERTY(dbo.TRY_CAST(212, 'INT', 0), 'BaseType') AS [BaseType];
SELECT dbo.TRY_CAST('AAAA0101', 'DATE', DEFAULT) AS [Cast failed]
, dbo.TRY_CAST('20160101', 'DATE', DEFAULT) AS [Cast succeeded]
, SQL_VARIANT_PROPERTY(dbo.TRY_CAST('2016-01-01', 'DATE', DEFAULT), 'BaseType') AS [BaseType];
SELECT dbo.TRY_CAST(1.23, 'NUMERIC(3,1)', DEFAULT) AS [Cast failed]
, dbo.TRY_CAST(12.3, 'NUMERIC(3,1)', DEFAULT) AS [Cast succeeded]
, SQL_VARIANT_PROPERTY(dbo.TRY_CAST(12.3, 'NUMERIC(3,1)', DEFAULT), 'BaseType') AS [BaseType];
SELECT dbo.TRY_CAST('A', 'BIT', DEFAULT) AS [Cast failed]
, dbo.TRY_CAST(1, 'BIT', DEFAULT) AS [Cast succeeded]
, SQL_VARIANT_PROPERTY(dbo.TRY_CAST('123', 'BIT', DEFAULT), 'BaseType') AS [BaseType];
GO
--E. B. TRY_CAST return NULL on unsupported data_types
SELECT dbo.TRY_CAST(4, 'xml', DEFAULT) AS [unsupported];
GO
====================================================================================================
------------------------------------------------------------------------------------------------------------------------
Responsible: Javier Pardo
Date: diciembre 29/2016
WB tests: Javier Pardo
------------------------------------------------------------------------------------------------------------------------
Update by: Javier Eduardo Pardo Moreno
Date: febrero 16/2017
Id update: JEPM20170216
Description: Fix ISNUMERIC function makes it unreliable. SELECT dbo.TRY_CAST('+', 'INT', 0) will yield Msg 8114,
Level 16, State 5, Line 16 Error converting data type varchar to float.
ISNUMERIC() function treats few more characters as numeric, like: – (minus), + (plus), $ (dollar), \ (back slash), (.)dot and (,)comma
Collaborator aperiooculus (http://stackoverflow.com/users/3083382/aperiooculus )
Fix dbo.TRY_CAST('2013/09/20', 'datetime', DEFAULT) for supporting DATETIME format
WB tests: Javier Pardo
------------------------------------------------------------------------------------------------------------------------
*/
ALTER FUNCTION dbo.TRY_CAST
(
@pExpression AS VARCHAR(8000),
@pData_Type AS VARCHAR(8000),
@pReturnValueIfErrorCast AS SQL_VARIANT = NULL
)
RETURNS SQL_VARIANT
AS
BEGIN
--------------------------------------------------------------------------------
-- INT
--------------------------------------------------------------------------------
IF @pData_Type = 'INT'
BEGIN
IF ISNUMERIC(@pExpression) = 1 AND @pExpression NOT IN ('-','+','$','.',',','\') --JEPM20170216
BEGIN
DECLARE @pExpressionINT AS FLOAT = CAST(@pExpression AS FLOAT)
IF @pExpressionINT BETWEEN - 2147483648.0 AND 2147483647.0
BEGIN
RETURN CAST(@pExpressionINT as INT)
END
ELSE
BEGIN
RETURN @pReturnValueIfErrorCast
END --FIN IF @pExpressionINT BETWEEN - 2147483648.0 AND 2147483647.0
END
ELSE
BEGIN
RETURN @pReturnValueIfErrorCast
END -- FIN IF ISNUMERIC(@pExpression) = 1
END -- FIN IF @pData_Type = 'INT'
--------------------------------------------------------------------------------
-- DATE
--------------------------------------------------------------------------------
IF @pData_Type IN ('DATE','DATETIME')
BEGIN
IF ISDATE(@pExpression) = 1
BEGIN
DECLARE @pExpressionDATE AS DATETIME = cast(@pExpression AS DATETIME)
IF @pData_Type = 'DATE'
BEGIN
RETURN cast(@pExpressionDATE as DATE)
END
IF @pData_Type = 'DATETIME'
BEGIN
RETURN cast(@pExpressionDATE as DATETIME)
END
END
ELSE
BEGIN
DECLARE @pExpressionDATEReplaced AS VARCHAR(50) = REPLACE(REPLACE(REPLACE(@pExpression,'\',''),'/',''),'-','')
IF ISDATE(@pExpressionDATEReplaced) = 1
BEGIN
IF @pData_Type = 'DATE'
BEGIN
RETURN cast(@pExpressionDATEReplaced as DATE)
END
IF @pData_Type = 'DATETIME'
BEGIN
RETURN cast(@pExpressionDATEReplaced as DATETIME)
END
END
ELSE
BEGIN
RETURN @pReturnValueIfErrorCast
END
END --FIN IF ISDATE(@pExpression) = 1
END --FIN IF @pData_Type = 'DATE'
--------------------------------------------------------------------------------
-- NUMERIC
--------------------------------------------------------------------------------
IF @pData_Type LIKE 'NUMERIC%'
BEGIN
IF ISNUMERIC(@pExpression) = 1
BEGIN
DECLARE @TotalDigitsOfType AS INT = SUBSTRING(@pData_Type,CHARINDEX('(',@pData_Type)+1, CHARINDEX(',',@pData_Type) - CHARINDEX('(',@pData_Type) - 1)
, @TotalDecimalsOfType AS INT = SUBSTRING(@pData_Type,CHARINDEX(',',@pData_Type)+1, CHARINDEX(')',@pData_Type) - CHARINDEX(',',@pData_Type) - 1)
, @TotalDigitsOfValue AS INT
, @TotalDecimalsOfValue AS INT
, @TotalWholeDigitsOfType AS INT
, @TotalWholeDigitsOfValue AS INT
SET @pExpression = REPLACE(@pExpression, ',','.')
SET @TotalDigitsOfValue = LEN(REPLACE(@pExpression, '.',''))
SET @TotalDecimalsOfValue = CASE Charindex('.', @pExpression)
WHEN 0
THEN 0
ELSE Len(Cast(Cast(Reverse(CONVERT(VARCHAR(50), @pExpression, 128)) AS FLOAT) AS BIGINT))
END
SET @TotalWholeDigitsOfType = @TotalDigitsOfType - @TotalDecimalsOfType
SET @TotalWholeDigitsOfValue = @TotalDigitsOfValue - @TotalDecimalsOfValue
-- The total digits can not be greater than the p part of NUMERIC (p, s)
-- The total of decimals can not be greater than the part s of NUMERIC (p, s)
-- The total digits of the whole part can not be greater than the subtraction between p and s
IF (@TotalDigitsOfValue <= @TotalDigitsOfType) AND (@TotalDecimalsOfValue <= @TotalDecimalsOfType) AND (@TotalWholeDigitsOfValue <= @TotalWholeDigitsOfType)
BEGIN
DECLARE @pExpressionNUMERIC AS FLOAT
SET @pExpressionNUMERIC = CAST (ROUND(@pExpression, @TotalDecimalsOfValue) AS FLOAT)
RETURN @pExpressionNUMERIC --Returns type FLOAT
END
else
BEGIN
RETURN @pReturnValueIfErrorCast
END-- FIN IF (@TotalDigitisOfValue <= @TotalDigits) AND (@TotalDecimalsOfValue <= @TotalDecimals)
END
ELSE
BEGIN
RETURN @pReturnValueIfErrorCast
END --FIN IF ISNUMERIC(@pExpression) = 1
END --IF @pData_Type LIKE 'NUMERIC%'
--------------------------------------------------------------------------------
-- BIT
--------------------------------------------------------------------------------
IF @pData_Type LIKE 'BIT'
BEGIN
IF ISNUMERIC(@pExpression) = 1
BEGIN
RETURN CAST(@pExpression AS BIT)
END
ELSE
BEGIN
RETURN @pReturnValueIfErrorCast
END --FIN IF ISNUMERIC(@pExpression) = 1
END --IF @pData_Type LIKE 'BIT'
--------------------------------------------------------------------------------
-- FLOAT
--------------------------------------------------------------------------------
IF @pData_Type LIKE 'FLOAT'
BEGIN
IF ISNUMERIC(REPLACE(REPLACE(@pExpression, CHAR(13), ''), CHAR(10), '')) = 1
BEGIN
RETURN CAST(@pExpression AS FLOAT)
END
ELSE
BEGIN
IF REPLACE(@pExpression, CHAR(13), '') = '' --Only white spaces are replaced, not new lines
BEGIN
RETURN 0
END
ELSE
BEGIN
RETURN @pReturnValueIfErrorCast
END --IF REPLACE(@pExpression, CHAR(13), '') = ''
END --FIN IF ISNUMERIC(@pExpression) = 1
END --IF @pData_Type LIKE 'FLOAT'
--------------------------------------------------------------------------------
-- Any other unsupported data type will return NULL or the value assigned by the user to @pReturnValueIfErrorCast
--------------------------------------------------------------------------------
RETURN @pReturnValueIfErrorCast
END
目前仅支持数据类型INT、DATE、DATETIME、NUMERIC、BIT 和 FLOAT。您可以在下面的下一个链接中找到此代码的最新版本，我们互相帮助改进它。SQL Server 2008 的 TRY_CAST 函数 https://gist.github.com/jotapardo/800881eba8c5072eb8d99ce6eb74c8bb
终于在 SO 和 Google 的帮助下找到了如何制作它。
更新声明：
UPDATE PriceTerm
SET PercentAddition = CONVERT(decimal(28,10), RTRIM(LTRIM(REPLACE(REPLACE(REPLACE(AdditionalDescription,'%',''), ',','.'), '&', ''))))
WHERE AdditionalDescription LIKE '%[%]%' AND
dbo.isreallynumeric(RTRIM(LTRIM(REPLACE(REPLACE(REPLACE(AdditionalDescription,'%',''), ',','.'), '&', '')))) = 1 AND
PercentAddition = 0
首先，我在大多数情况下搜索 % char 作为百分比值的标记。但也有随机的其他用途。事实证明，ISNUMERIC 在我的情况下并不可靠。
真正不同的是从这里调用存储过程 isreallynumeric 。
所以
CREATE FUNCTION dbo.isReallyNumeric
(
@num VARCHAR(64)
)
RETURNS BIT
BEGIN
IF LEFT(@num, 1) = '-'
SET @num = SUBSTRING(@num, 2, LEN(@num))
DECLARE @pos TINYINT
SET @pos = 1 + LEN(@num) - CHARINDEX('.', REVERSE(@num))
RETURN CASE
WHEN PATINDEX('%[^0-9.-]%', @num) = 0
AND @num NOT IN ('.', '-', '+', '^')
AND LEN(@num)>0
AND @num NOT LIKE '%-%'
AND
(
((@pos = LEN(@num)+1)
OR @pos = CHARINDEX('.', @num))
)
THEN
1
ELSE
0
END
END
GO
我更喜欢简单的解决方案，并制作了如下所示的 SP。
CREATE PROC TRY_CAST
(
@valueToBeParsed VARCHAR(64), @parsedValue INT OUTPUT
)
AS
BEGIN
BEGIN TRY
SELECT @parsedValue = cast(@valueToBeParsed as int)
END TRY
BEGIN CATCH
SET @parsedValue = null
END CATCH
END
GO
并像下面一样使用它
DECLARE @val int
EXEC TRY_CAST '1w', @val out
select @val
CASE WHEN ISNUMERIC(yourColumn) = 1
THEN CAST(yourColumn AS DECIMAL(28,10))
ELSE NULL --or Zero
END AS yourColumName
2019 年，仍然使用 2008 年的服务器，所以我有同样的问题。以上对我有用。
SQL SERVER 2008 R2 有一个函数 TRY_CAST 但如果您将数据库配置为与 2005 兼容，您会发现 SQL SERVER 无法识别它。
我使用了创建@jotapardo但重命名 TRY_CAST2 的函数，因为在这种情况下 SS 识别了函数。