在SQL Server 2008中获取相同输出的最简单方法是什么？
SQLServer 2012：
select
try_parse(Isnull('123.66',0) as float) as a ,
try_parse(Isnull('.',0) as float) as b
结果
a b
------------
123.66 NULL
SQLServer 2008： ？
答案 0 :(得分：4)
TRY_PARSE做两件事 - 使用特定文化解析文本，如果转换失败则返回NULL。在SQL Server 2008中，您可以使用ISNUMERIC函数模拟此功能的一部分，如shown here：
select
CASE
WHEN ISNUMERIC(@input)=1 and LEFT(@input,1) LIKE'[0-9]' THEN
CAST(@input as float)
ELSE
NULL
END,
ISNUMERIC即使对于.或“.5”也会返回1，导致演员表失败。第二次检查LEFT(@input,1) LIKE'[0-9]'
您可以创建标量函数，这样您就不必在每次要转换值时都输入所有这些：
CREATE FUNCTION try_parse_float(@input varchar(20))
returns float
AS
begin
declare @result float;
select @result=CASE
WHEN ISNUMERIC(@input)=1 and LEFT(@input,1) LIKE'[0-9]'
THEN CAST(@input as float)
ELSE NULL
END;
return @result;
end
所以你可以写
SELECT dbo.try_parse_float('123,4'), try_parse_float('.')
----- ----
123.4 NULL
修改
最安全和最快的选择是简单地避免将数值作为文本存储在数据库中，确保在加载期间解析数据。例如，.NET和OLEDB提供程序可以将"123-"解析为-123，而T-SQL则不能。
在加载过程中处理自定义格式也更容易，例如在将表单数据保存到数据库之前使用float.TryParseExact调用，或者在SSIS ETL脚本中使用C＃Script组件。
答案 1 :(得分：1)
我编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)
与SQL Server 2012的TRY_CAST功能的两个主要区别在于您必须传递3个参数 必须另外对该字段执行显式CONVERT或CAST。 但是，它仍然非常有用，因为它允许你返回一个 如果未正确执行CAST，则为默认值。
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
------------------------------------------------------------------------------------------------------------------------
*/
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
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 = 'DATE'
BEGIN
IF ISDATE(@pExpression) = 1
BEGIN
DECLARE @pExpressionDATE AS DATE = cast(@pExpression AS DATE)
RETURN cast(@pExpressionDATE as DATE)
END
ELSE
BEGIN
RETURN @pReturnValueIfErrorCast
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，NUMERIC，BIT和FLOAT 。您可以在下面的下一个链接中找到此代码的最后一个版本，我们互相帮助以改进它。 SQL Server 2008的TRY_CAST函数 https://gist.github.com/jotapardo/800881eba8c5072eb8d99ce6eb74c8bb
答案 2 :(得分：-1)
你可以使用这个代码片段来完成你想要的东西。 将它添加到更大的表上的选择中应该不是什么大不了的事。只需用代码列替换变量即可。
以下是示例：
DECLARE @string nvarchar(255)
SET @string = 'Hali€hHalo'
SELECT Substring(
@string,
PATINDEX('%[0-9.]%',@string),
PATINDEX('%[^0-9.]%',
Substring(
@string,
PATINDEX(
'%[0-9.]%',
@string
),
LEN(@string)
)
)-1
)
GO
结果：空字符串，但是这可以用CASE WHEN替换... IS NULL THEN NULL ELSE ... END如果需要NULL。
与带数字的变量相同。
DECLARE @string nvarchar(255)
SET @string = 'Hali123.10€hHalo'
SELECT Substring(
@string,
PATINDEX('%[0-9.]%',@string),
PATINDEX('%[^0-9.]%',
Substring(
@string,
PATINDEX(
'%[0-9.]%',
@string
),
LEN(@string)
)
)-1
)
GO
结果：123.10
祝你好运， 离子