如何使用ADO和VB将NULL或空字符串传递给存储过程输入参数？ [英] How to pass NULL or empty strings to stored procedure input parameter with ADO and VB?

问题描述

我在Sql Server 2005中有一个存储过程，其varchar输入参数定义为：

I have a stored procedure in Sql Server 2005 with a varchar input parameter defined as:

@Value varchar(24) = NULL

在我的VB6应用程序中，我尝试使用ADO函数设置参数：

in my VB6 application I try to set the parameter with an ADO function:

Set prmParamVal = cmdChkParam.CreateParameter(, adVarChar, adParamInput, Len(paramValue), paramValue)

如果我尝试传递的值是一个空（零长度）字符串，则出现以下错误：

If the value I try to pass is an empty (zero length) string, then I get the following error:

ADODB。连接错误'800a0e7c'
参数对象定义不正确。提供的信息不一致或不完整。

ADODB.Connection error '800a0e7c' Parameter object is improperly defined. Inconsistent or incomplete information was provided.

我试图传递NULL值而不是空字符串，但这会导致不同的错误。

I tried to pass a NULL value instead of the empty string, but this lead to different errors.

如何将空字符串或NULL值传递给存储过程？

How can I pass empty strings or NULL values to the stored procedure?

我已经读了很多文章和搜索的论坛（甚至多次找到我的问题），但没有正确的答案。

I already read a lot of articles and searched forums (even found my question several times) but without the right answer.

到目前为止，对于空字符串的解决方法是将length设置为1或set字符串=（空格）。但这并不是很好，我希望发送NULL。我还尝试将paramValue设置为vbNull，Null，vbNullString或将prmParamVal.value =空设置为没有运气！

The workaround so far for the empty strings is to set the length = 1 or set the string = " " (a blank space). But thats not really nice and I would favour to send NULL. I also experimented with setting paramValue to vbNull, Null, vbNullString or to set prmParamVal.value = Empty without any luck!

推荐答案

A这里的快速测试表明NULL应该可以完成工作。我曾经测试的示例代码（到一个带有一个按钮和一个文本框的简单表单中）：

A quick test here shows that's NULL ought to do the job. Sample code I used to test (onto a simple form with one button and one textbox):

Private Sub Command1_Click()
    Dim dbConn As ADODB.Connection
    Dim dbComm As ADODB.Command
    Dim dbRS As ADODB.Recordset

    Set dbConn = New ADODB.Connection
    With dbConn
        .ConnectionString = "...REPLACE THIS ACCORDINGLY..."
        .ConnectionTimeout = 10
        .Open
    End With
    Set dbComm = New ADODB.Command
    With dbComm
        .ActiveConnection = dbConn
        .CommandType = adCmdStoredProc
        .CommandText = "usp_Bob"
        .Parameters.Append .CreateParameter("b", adVarChar, adParamInput, 10, Null)
        Set dbRS = .Execute
    End With
    Text1.Text = dbRS.Fields.Item(0).Value

    dbRS.Close
    dbConn.Close
End Sub

它调用了此存储过程：

ALTER PROCEDURE usp_Bob
 @b VARCHAR(10)
AS
 IF @b IS NULL
  SELECT 'NULL' AS '1'
 ELSE
  IF @b = ''
   SELECT 'EMPTY' AS '1'
  ELSE
   SELECT 'NOT NULL AND NOT EMPTY' AS '1'

usp_Bob由于使用VB值 Null （根据上面的示例）而返回'NULL'，而'NOT' vbNull 为NULL。如果 Null 对您不起作用，那么我无法评论可能是什么问题...！

usp_Bob returned 'NULL' for using the VB value Null (as per the sample above), and 'NOT NULL' for vbNull. If Null doesn't work for you, then I can't comment on what might be wrong...!

类似地，应该像这样传递空字符串-一个空字符串，即 str = -这会使usp_Bob返回'EMPTY'。

Similarly, empty strings should be passed just as that -- an empty string, i.e. str = "" -- which makes usp_Bob return 'EMPTY'. Anything else has it return 'NOT NULL AND NOT EMPTY' (as expected).

如果您无法通过NULL，那么另一种选择是将其强制转换为空。在程序中将字符串转换为NULL-即

If you can't get NULL passed through, then another option is to cast an empty string to NULL in the sproc -- i.e.,

IF @param = ''
    SET @param = NULL

请注意，经过的长度并不太重要。这反映了SQL Server中定义的参数的最大长度，而不是您正在传递的数据的长度。

Note that the length you pass through shouldn't matter too much. It's a reflection of the maximum length of the parameter as defined in SQL Server rather than the length of the data you're passing through.

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