我编写了一个有用的标量函数，用于在SQL Server 2008中模拟SQL SERVER 2012的TRY_CAST函数。
dbo.TRY_CAST(Expression, Data_Type, ReturnValueIfErrorCast)
TRY_CAST函数在SQL Server 2012中有两个主要的区别，你必须传递3个参数，并且你还必须显式地将转换或转型应用到字段上。然而，它仍然非常有用，因为它允许你在转型未能正确执行时返回一个默认值。
函数代码：
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
ALTER FUNCTION dbo.TRY_CAST
(
@pExpression AS VARCHAR(8000),
@pData_Type AS VARCHAR(8000),
@pReturnValueIfErrorCast AS SQL_VARIANT = NULL
)
RETURNS SQL_VARIANT
AS
BEGIN
IF @pData_Type = 'INT'
BEGIN
IF ISNUMERIC(@pExpression) = 1 AND @pExpression NOT IN ('-','+','$','.',',','\')
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
END
ELSE
BEGIN
RETURN @pReturnValueIfErrorCast
END
END
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
END
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
IF (@TotalDigitsOfValue <= @TotalDigitsOfType) AND (@TotalDecimalsOfValue <= @TotalDecimalsOfType) AND (@TotalWholeDigitsOfValue <= @TotalWholeDigitsOfType)
BEGIN
DECLARE @pExpressionNUMERIC AS FLOAT
SET @pExpressionNUMERIC = CAST (ROUND(@pExpression, @TotalDecimalsOfValue) AS FLOAT)
RETURN @pExpressionNUMERIC
END
else
BEGIN
RETURN @pReturnValueIfErrorCast
END
END
ELSE
BEGIN
RETURN @pReturnValueIfErrorCast
END
END
IF @pData_Type LIKE 'BIT'
BEGIN
IF ISNUMERIC(@pExpression) = 1
BEGIN
RETURN CAST(@pExpression AS BIT)
END
ELSE
BEGIN
RETURN @pReturnValueIfErrorCast
END
END
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), '') = ''
BEGIN
RETURN 0
END
ELSE
BEGIN
RETURN @pReturnValueIfErrorCast
END
END
END
RETURN @pReturnValueIfErrorCast
END
目前仅支持
INT、DATE、DATETIME、NUMERIC、BIT 和 FLOAT 数据类型。您可以在下面的链接中找到此代码的最新版本，并且我们可以相互帮助进行改进。
SQL Server 2008 的 TRY_CAST 函数。
https://gist.github.com/jotapardo/800881eba8c5072eb8d99ce6eb74c8bb
