visual basic数据库开发疑难问题解.txt

Visual Basic数据库开发疑难问题解 。

［前言：］我始终认为Visual Basic是数据库开发最便捷的工具，我在论坛中看到不少朋友提出的关于VB数据库开发方面的问题，有许多问题是反复提出，也有些我认为是比较典型的问题，我将这些问题收录在一起同时提出答案，便于网友们查阅，如果你还有社呢们提可以给我写信。

　　问：如何显示格式为03-3-13的日期？

　　解决的方法：

1　 
Cmd.CommandText = "select * from 支出 where 日期=03-3-13" 中 03-3-13=-13。
日期实际上是Double型数字。0 是 1899-12-30，-13 是 1899-12-17。你当然没有这样日期的记录，所以只有大于才行。 
2
Cmd.CommandText = "select * from 支出 where 日期=#03-3-13#"
凡是没有明示，文字型日期是按美国习惯解释的，#03-3-13# 是 0013-03-03。

或者使用长日期格式：
Cmd.CommandText = "select * from 支出 where 日期=#2003-3-13#"
用格式化函数：
Cmd.CommandText = "select * from 支出 where 日期=#" & format(mydate,"yyyy-mm-dd") & "#"
 

　　问： 如何判断DNS是否存在？怎样才能列举出所有的DNS?

　　解决方法：

　　1、通过利用ODBC API中的SQLDataSource函数可以取得ODBC API中数据源的列表。 判断DNS是否存在：
　 
　　2、使用API函数Private Declare Function SQLDataSources Lib "ODBC32.DLL" (ByVal henv As Long, ByVal fDirection As Integer, ByVal szDSN As String, ByVal cbDSNMax As Integer, pcbDSN As Integer, ByVal szDescription As String, ByVal cbDescriptionMax As Integer, pcbDescription As Integer) As Integer Private Declare Function SQLAllocEnv Lib "ODBC32.DLL" (ByRef env As Long) As Long 列举出所有DNS。 

　　问：处理文本文件是导入数据库还是直接读写文件呢？ 

　　解决方法：

Set main = bumony.OpenRecordset("main")
Open App.Path & "\sources\" & Text1.Text & "\′úàíòμ??" & Text1.Text & ".txt" For Input As #1
Do While Not EOF(1)
Line Input #1, str1
With main
.AddNew
!code = Mid(str1, 1, 5)
!date = Text1.Text
If Mid(str1, 1, 5) = "21310" Or Mid(str1, 1, 5) = "21311" Or Mid(str1, 1, 5) = "21410" Or Mid(str1, 1, 5) = "21411" Then
!Money = Trim(Mid(str1, 7, 10))
Else
!Money = Trim(Mid(str1, 7, 10)) & "0000"
End If
!whao = "1102"
!ywhao = "1102"
.Update
End With
Loop
Close #1
main.Close 

　　问：调用SQL存储后有参数返回,应该怎么赋值?

　　解决方法：


Dim ADOCmd As New ADODB.Command
Dim ADOPrm As New ADODB.Parameter
Dim ADORs As ADODB.Recordset

'....
Set ADOCmd.ActiveConnection = ADOCon
With ADOCmd
.CommandType = adCmdStoredProc
.CommandText = "ADOTestRPE"
End With

sParmName = "Output"
Set ADOPrm = ADOCmd.CreateParameter(sParmName, adInteger, adParamOutput)
ADOCmd.Parameters.Append ADOPrm
ADOCmd.Parameters(sParmName).Value = 999

Set ADORs = ADOCmd.Execute
'.....

Debug.Print "Output: " & ADOCmd.Parameters("Output").Value
 

　　问： SQL Server 2000中如何存取图片信息？ 
　　
　　解决方法:


新建一个工程,添加 ado 控件,2个 Command ,1个 Picture,1个 Image 

Dim Chunk() As Byte
Dim lngLengh As Long
Dim intChunks As Integer
Dim intFragment As Integer
Const ChunkSize = 1000
Const lngDataFile = 1

Private Sub cmdBrowse_Click()

On Error Resume Next
With cmdlFilePath
.Filter = "JPG Files|*.JPG|Bitmaps|*.BMP"
.ShowOpen
txtFilePath.Text = .filename
End With
End Sub

Private Sub Savepic()

Open "c:\colordraw0094_m.jpg" For Binary Access Read As lngDataFile
lngLengh = LOF(lngDataFile)
If lngLengh = 0 Then Close lngDatafile: Exit Sub
intChunks = lngLengh \ ChunkSize
intFragment = lngLengh Mod ChunkSize

'OpenData 打开数据库
Dim i As Integer
Dim rs As New ADODB.Recordset
Dim strQ As String

If rs.State = adStateOpen Then rs.Close

strQ = "Select * From [mydata]"
rs.Open strQ, conn, adOpenStatic, adLockOptimistic

On Error Resume Next

rs.AddNew

ReDim Chunk(intFragment)
Get lngDataFile, , Chunk()
rs.Fields("rs_photo1").AppendChunk Chunk()
ReDim Chunk(ChunkSize)

For i = 1 To intChunks
Get lngDataFile, , Chunk()
rs.Fields("rs_photo1").AppendChunk Chunk()
Next i

rs.Update
rs.Close
Close lngDataFile
Call ShowPic

End Sub

Public Sub ShowPic()

'OpenData 打开数据库
Dim i As Integer
Dim rs As New ADODB.Recordset
Dim strQ, filename As String
If rs.State = adStateOpen Then rs.Close

strQ = "Select * From [mydata]"
rs.Open strQ, conn, adOpenStatic, adLockOptimistic
If rs.EOF <> True Then
rs.MoveLast
Else
Exit Sub
End If
On Error Resume Next
Open "pictemp" For Binary Access Write As lngDataFile
lngLengh = rs.Fields("rs_photo1").ActualSize
intChunks = lngLengh \ ChunkSize
intFragment = lngLengh Mod ChunkSize
ReDim Chunk(intFragment)
Chunk() = rs.Fields("rs_photo1").GetChunk(intFragment)
Put lngDataFile, , Chunk()
For i = 1 To intChunks
ReDim Buffer(ChunkSize)
Chunk() = rs.Fields("rs_photo1").GetChunk(ChunkSize)
Put lngDataFile, , Chunk()
Next i
Close lngDataFile
filename = "pictemp"
Picture1.Picture = LoadPicture(filename)
Image1.Stretch = True
Image1.Picture = Picture1.Picture
Kill filename

End Sub

Private Sub Command1_Click()

Savepic

End Sub

Private Sub Command2_Click()

ShowPic

End Sub

上面写的是acess的代码!楼主可以改一下连接数据库的设置代码用于sql server!
 
问：如何在VB里做SQL的数据库的备份和恢复？

　　解决方法:


Option Explicit 

Private Const cnstr As String = "Provider=SQLOLEDB.1;Password=****;Persist Security Info=True;" _
& "User ID=*****;Initial Catalog=master;Data Source=******"

Private DBCn As ADODB.Connection

Private Sub cmdBackup_Click()
Set DBCn = New ADODB.Connection
DBCn.Open cnstr
DBCn.Execute "backup database pubs to disk='d:\pubs_backup.dat'"
DBCn.Close
End Sub

Private Sub cmdRestore_Click()
Set DBCn = New ADODB.Connection
DBCn.Open cnstr
DBCn.Execute "restore database pubs from disk='d:\pubs_backup.dat'"
DBCn.Close
End Sub
 

　　问：如何通过ADO获得数据库的字段名，字段类型？

　　解决方法：

　　名： recordset.fields(index).name 
类型：recordset.fields(index).type 
类型是用数字表示的，msdn上有对应表 
--------------------------------------------------------------- 

OpenSchema 方法 


从提供者获取数据库模式信息。 

语法 

Set recordset = connection.OpenSchema (QueryType, Criteria, SchemaID) 

返回值 

返回包含模式信息的 Recordset 对象。Recordset 将以只读、静态游标打开。 

参数 

QueryType 所要运行的模式查询类型，可以为下列任意常量。 

Criteria 可选。每个 QueryType 选项的查询限制条件数组，如下所列： 

QueryType 值 Criteria 值 
AdSchemaAsserts CONSTRAINT_CATALOG 
CONSTRAINT_SCHEMA 
CONSTRAINT_NAME 
AdSchemaCatalogs CATALOG_NAME 
AdSchemaCharacterSets CHARACTER_SET_CATALOG 
CHARACTER_SET_SCHEMA 
CHARACTER_SET_NAME 
AdSchemaCheckConstraints CONSTRAINT_CATALOG 
CONSTRAINT_SCHEMA 
CONSTRAINT_NAME 
AdSchemaCollations COLLATION_CATALOG 
COLLATION_SCHEMA 
COLLATION_NAME 
AdSchemaColumnDomainUsage DOMAIN_CATALOG 
DOMAIN_SCHEMA 
DOMAIN_NAME 
COLUMN_NAME 
AdSchemaColumnPrivileges TABLE_CATALOG 
TABLE_SCHEMA 
TABLE_NAME 
COLUMN_NAME 
GRANTOR 
GRANTEE 
adSchemaColumns TABLE_CATALOG 
TABLE_SCHEMA 
TABLE_NAME 
COLUMN_NAME 
adSchemaConstraintColumnUsage TABLE_CATALOG 
TABLE_SCHEMA 
TABLE_NAME 
COLUMN_NAME 
adSchemaConstraintTableUsage TABLE_CATALOG 
TABLE_SCHEMA 
TABLE_NAME 
adSchemaForeignKeys PK_TABLE_CATALOG 
PK_TABLE_SCHEMA 
PK_TABLE_NAME 
FK_TABLE_CATALOG 
FK_TABLE_SCHEMA 
FK_TABLE_NAME 
adSchemaIndexes TABLE_CATALOG 
TABLE_SCHEMA 
INDEX_NAME 
TYPE 
TABLE_NAME 
adSchemaKeyColumnUsage CONSTRAINT_CATALOG 
CONSTRAINT_SCHEMA 
CONSTRAINT_NAME 
TABLE_CATALOG 
TABLE_SCHEMA