vb.net 中 sql查询出来的值，比如books中的remainnum,赋给一个变量 num，再将num-1之后update到remainnum中

Dim num As Integer

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Dim connstr, insertcmd, selectcmd As String

connstr = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=D:\360data\重要数据\我的文档\hd.mdb"

Dim conn As OleDbConnection

Dim cmd, cmd1 As OleDbCommand

conn = New OleDbConnection(connstr)

Dim r As OleDbDataReader

conn.Open()

insertcmd = "insert into returnbooks (aid,aname,ISBN,bname,renum,reday) values("

Val(ComboBox1.Text) ",'"

TextBox2.Text "','"

ComboBox2.Text "','"

TextBox2.Text "',"

Val(TextBox3.Text) ",'"

CType(TextBox4.Text, Date) "' )"

cmd = New OleDbCommand(insertcmd, conn)

cmd.ExecuteNonQuery()

updatecmd = "update books set remainnum=" Val(num) "-" Val(TextBox3.Text) " where ISBN='" ComboBox2.Text "'"

cmd = New OleDbCommand(updatecmd, conn)

cmd.ExecuteNonQuery()

updatecmd = "select remainnum as num from books where ISBN= '" ComboBox2.Text "'"

cmd = New OleDbCommand(updatecmd, conn)

cmd.ExecuteNonQuery()

updatecom = "update books set remainnum=num+ " Val(TextBox3.Text) ""

cmd = New OleDbCommand(updatecmd, conn)

cmd.ExecuteNonQuery()

selectcmd = "select remainnum from books where ISBN='" ComboBox2.Text "'"

cmd1 = New OleDbCommand(selectcmd, conn)

r = cmd1.ExecuteReader()

If (r.Read()) Then '如果sql查询到了数据

num = r.GetInt32(0)

End If

conn.Close()

/*注意代码的格式，不然改起来太费时间*/

求《VB.net入门经典（第四版）》电子书

电子书太大，发布过去，楼主可以到网站上下载

;restype=-1id=10000001ty=0

求VB.NET 参考文献

中文的话，这里有个网站你可以去看看，上面搜罗了很多相关的书，

如果是英语的话，《Beginning VB.NET 2003》，作者：Thearon Willis, Jonathan Crossland, Richard Blair,其他信息：Wrox（出版社）; 3 Sub edition | ISBN:0764556584 | 840 pages | April 9, 2004 | CHM | 32 Mb

vb.net操作xml数据库(急)

使用System.XML

Imports Microsoft.VisualBasic

Imports System

Imports System.IO

Imports System.Xml

namespace HowTo.Samples.XML

public class WriteXmlFileSample

private const document as string = "newbooks.xml"

shared sub Main()

Dim myWriteXmlFileSample as WriteXmlFileSample

myWriteXmlFileSample = new WriteXmlFileSample()

myWriteXmlFileSample.Run(document)

end sub

public sub Run(args As String)

Dim myXmlTextReader as XmlTextReader = nothing

Dim myXmlTextWriter as XmlTextWriter = nothing

try

myXmlTextWriter = new XmlTextWriter (args, nothing)

myXmlTextWriter.Formatting = System.Xml.Formatting.Indented

myXmlTextWriter.WriteStartDocument(false)

myXmlTextWriter.WriteDocType("bookstore", nothing, "books.dtd", nothing)

myXmlTextWriter.WriteComment("此文件表示书店库存数据库的另一个片断")

myXmlTextWriter.WriteStartElement("bookstore")

myXmlTextWriter.WriteStartElement("book", nothing)

myXmlTextWriter.WriteAttributeString("genre","autobiography")

myXmlTextWriter.WriteAttributeString("publicationdate","1979")

myXmlTextWriter.WriteAttributeString("ISBN","0-7356-0562-9")

myXmlTextWriter.WriteElementString("title", nothing, "The Autobiography of Mark Twain")

myXmlTextWriter.WriteStartElement("Author", nothing)

myXmlTextWriter.WriteElementString("first-name", "Mark")

myXmlTextWriter.WriteElementString("last-name", "Twain")

myXmlTextWriter.WriteEndElement()

myXmlTextWriter.WriteElementString("price", "7.99")

myXmlTextWriter.WriteEndElement()

myXmlTextWriter.WriteEndElement()

'向文件写 XML 并关闭编写器

myXmlTextWriter.Flush()

myXmlTextWriter.Close()

' 读取返回的文件并进行分析以确保正确生成 XML

myXmlTextReader = new XmlTextReader (args)

FormatXml (myXmlTextReader, args)

catch e as Exception

Console.WriteLine ("异常：{0}", e.ToString())

finally

Console.WriteLine()

Console.WriteLine("对文件 {0} 的处理已完成。", args)

If Not myXmlTextReader Is Nothing

myXmlTextReader.Close()

end if

'关闭编写器

If Not myXmlTextWriter Is Nothing

myXmlTextWriter.Close()

end if

End try

End Sub

private shared Sub FormatXml (reader as XmlTextReader, filename as String)

Dim piCount, docCount, commentCount, elementCount as Integer

Dim attributeCount, textCount, whitespaceCount as Integer

While reader.Read()

Select (reader.NodeType)

case XmlNodeType.ProcessingInstruction:

Format (reader, "ProcessingInstruction")

piCount += 1

case XmlNodeType.DocumentType:

Format (reader, "DocumentType")

docCount += 1

case XmlNodeType.Comment:

Format (reader, "Comment")

commentCount += 1

case XmlNodeType.Element:

Format (reader, "Element")

elementCount += 1

While reader.MoveToNextAttribute()

Format (reader, "Attribute")

end While

if (reader.HasAttributes)

attributeCount += reader.AttributeCount

end if

case XmlNodeType.Text:

Format (reader, "Text")

textCount += 1

case XmlNodeType.Whitespace:

whitespaceCount += 1

End Select

End While

' 显示该文件的统计信息

Console.WriteLine ()

Console.WriteLine("{0} 文件的统计信息", filename)

Console.WriteLine ()

Console.WriteLine("处理指令：" piCount)

Console.WriteLine("文档类型：" docCount)

Console.WriteLine("注释：" commentCount)

Console.WriteLine("元素：" elementCount)

Console.WriteLine("属性：" attributeCount)

Console.WriteLine("文本：" textCount)

Console.WriteLine("空白：" whitespaceCount)

End Sub

private shared Sub Format(byref reader as XmlTextReader , NodeType as String)

' 格式化输出

Console.Write(reader.Depth " ")

Console.Write(reader.AttributeCount " ")

Dim i as Integer

for i = 0 to reader.Depth - 1

Console.Write(Strings.chr(9))

Next

Console.Write(reader.Prefix NodeType "" reader.Name "" reader.Value)

Console.WriteLine()

End Sub

End Class

End Namespace

参考: