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 & "/´úÀíÒµÎñ" & 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
[责任编辑:editor]
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!
[责任编辑:editor]
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
TABLE_NAME
COLUMN_NAME
adSchemaPrimaryKeys PK_TABLE_CATALOG
PK_TABLE_SCHEMA
PK_TABLE_NAME
adSchemaProcedureColumns PROCEDURE_CATALOG
PROCEDURE_SCHEMA
PROCEDURE_NAME
COLUMN_NAME
adSchemaProcedureParameters PROCEDURE_CATALOG
PROCEDURE_SCHEMA
PROCEDURE_NAME
PARAMTER_NAME
adSchemaProcedures PROCEDURE_CATALOG
PROCEDURE_SCHEMA
PROCEDURE_NAME
PROCEDURE_TYPE
adSchemaProviderSpecific 参见说明
adSchemaProviderTypes DATA_TYPE
BEST_MATCH
adSchemaReferentialConstraints CONSTRAINT_CATALOG
CONSTRAINT_SCHEMA
CONSTRAINT_NAME
adSchemaSchemata CATALOG_NAME
SCHEMA_NAME
SCHEMA_OWNER
adSchemaSQLLanguages <无>
adSchemaStatistics TABLE_CATALOG
TABLE_SCHEMA
TABLE_NAME
adSchemaTableConstraints CONSTRAINT_CATALOG
CONSTRAINT_SCHEMA
CONSTRAINT_NAME
TABLE_CATALOG
TABLE_SCHEMA
TABLE_NAME
CONSTRAINT_TYPE
adSchemaTablePrivileges TABLE_CATALOG
TABLE_SCHEMA
TABLE_NAME
GRANTOR
GRANTEE
adSchemaTables TABLE_CATALOG
TABLE_SCHEMA
TABLE_NAME
TABLE_TYPE
adSchemaTranslations TRANSLATION_CATALOG
TRANSLATION_SCHEMA
TRANSLATION_NAME
adSchemaUsagePrivileges OBJECT_CATALOG
OBJECT_SCHEMA
OBJECT_NAME
OBJECT_TYPE
GRANTOR
GRANTEE
adSchemaViewColumnUsage VIEW_CATALOG
VIEW_SCHEMA
VIEW_NAME
adSchemaViewTableUsage VIEW_CATALOG
VIEW_SCHEMA
VIEW_NAME
adSchemaViews TABLE_CATALOG
TABLE_SCHEMA
TABLE_NAME
SchemaID OLE DB 规范没有定义用于提供者模式查询的 GUID。如果 QueryType 设置为 adSchemaProviderSpecific，则需要该参数，否则不使用它。
说明
OpenSchema 方法返回与数据源有关的信息，例如关于服务器上的表以及表中的列等信息。
Criteria 参数是可用于限制模式查询结果的值数组。每个模式查询有它支持的不同参数集。实际模式由 IDBSchemaRowset 接口下的 OLE DB 规范定义。ADO 中所支持的参数集已在上面列出。
如果提供者定义未在上面列出的非标准模式查询，则常量 adSchemaProviderSpecific 将用于 QueryType 参数。在使用该常量时需要 SchemaID 参数传递模式查询的 GUID 以用于执行。如果 QueryType 设置为 adSchemaProviderSpecific 但是没有提供 SchemaID，将导致错误。
提供者不需要支持所有的 OLE DB 标准模式查询，只有 adSchemaTables、adSchemaColumns 和 adSchemaProviderTypes 是 OLE DB 规范需要的。但是对于这些模式查询，提供者不需要支持上面列出的 Criteria 条件约束。
远程数据服务用法 OpenSchema 方法在客户端 Connection 对象上无效。
注意 在 Visual Basic 中，在由 Connection 对象的 OpenSchema 方法所返回的 Recordset 中有 4 字节无符号整型 (DBTYPE UI4) 的列无法与其他变量比较。有关 OLE DB 数据类型的详细信息，请参阅“Microsoft OLE DB 程序员参考”的第十章和附录 A。
---------------------------------------------------------------
OpenSchema 方法范例
该范例使用 OpenSchema 方法显示 Pubs 数据库内每个表的名称和类型。
Public Sub OpenSchemaX()
Dim cnn1 As ADODB.Connection
Dim rstSchema As ADODB.Recordset
Dim strCnn As String
Set cnn1 = New ADODB.Connection
strCnn = "Provider=sqloledb;" & _
"Data Source=srv;Initial Catalog=pubs;User Id=sa;Password=; "
cnn1.Open strCnn
Set rstSchema = cnn1.OpenSchema(adSchemaTables)
Do Until rstSchema.EOF
Debug.Print "Table name: " & _
rstSchema!TABLE_NAME & vbCr & _
"Table type: " & rstSchema!TABLE_TYPE & vbCr
rstSchema.MoveNext
Loop
rstSchema.Close
cnn1.Close
End Sub
该范例在 OpenSchema 方法的 Criteria 参数中指定 TABLE_TYPE 查询约束。因此，只返回在 Pubs 数据库中指定视图的模式信息。然后该范例显示每个表的名称和类型。
Public Sub OpenSchemaX2()
Dim cnn2 As ADODB.Connection
Dim rstSchema As ADODB.Recordset
Dim strCnn As String
Set cnn2 = New ADODB.Connection
strCnn = "Provider=sqloledb;" & _
"Data Source=srv;Initial Catalog=pubs;User Id=sa;Password=; "
cnn2.Open strCnn
Set rstSchema = cnn2.OpenSchema(adSchemaTables, Array(Empty, Empty, Empty, "VIEW"))
Do Until rstSchema.EOF
Debug.Print "Table name: " & _
rstSchema!TABLE_NAME & vbCr & _
"Table type: " & rstSchema!TABLE_TYPE & vbCr
rstSchema.MoveNext
Loop
rstSchema.Close
cnn2.Close
End Sub
---------------------------------------------------------------
ado的recordset 对象在返回记录集时，同时也有各字段的名字和类型。
具体是：recordset.Fields.Item(i).Name
recordset.Fields.Item(i).Type
类型是枚举型，你可以查对应的值
还有其它属性：
recordset.Fields.Item(i).DefinedSize 字段的定义宽度
recordset.Fields.Item(i).ActualSize 字段的实际宽度
....
---------------------------------------------------------------
其他我不想再说了，看我用过的：
for i=0 to rs.recordcount-1
print rs.Fields(i).Name & " " & rs.Fields(i).Type "(" & rs.Fields(i).ActualSize & ")"
next
---------------------------------------------------------------
Private Sub Command1_Click()
Dim Cn As New ADODB.Connection
Dim Rs_Table As New ADODB.Recordset
Dim Rs_Colums As New ADODB.Recordset
With Cn '定义连接
.CursorLocation = adUseClient
.Provider = "sqloledb"
.Properties("Data Source").Value = "LIHG"
.Properties("Initial Catalog").Value = "NorthWind"
.Properties("User ID") = "sa"
.Properties("Password") = "sa"
.Properties("prompt") = adPromptNever
.ConnectionTimeout = 15
.Open
If .State = adStateOpen Then
Rs_Table.CursorLocation = adUseClient '得到所有表名
Rs_Table.Open "SELECT name From sysobjects WHERE xtype = 'u'", Cn, adOpenDynamic, adLockReadOnly
Rs_Table.MoveFirst
Do While Not Rs_Table.EOF
Debug.Print Rs_Table.Fields("name")
Rs_Colums.CursorLocation = adUseClient
Rs_Colums.Open "select * from [" & Rs_Table.Fields("name") & "]", Cn, adOpenStatic, adLockReadOnly
For I = 0 To Rs_Colums.Fields.Count - 1 ' 循环所有列
Debug.Print Rs_Colums.Fields(I).Name '字段名
Debug.Print FieldType(Rs_Colums.Fields(I).Type) '字段类型
Debug.Print Rs_Colums.Fields(I).DefinedSize '宽度
Next
Rs_Colums.Close
[责任编辑:editor]
问：怎么把Sqlserver 的数据转换并输出成Xml格式文件？
解决方法:
SQL Server7的用法
Private Sub Command1_Click()
Dim strmResults As New ADODB.Stream
Dim cn As New ADODB.Connection
Dim cmd As New ADODB.Command
Dim cnstr As String
cnstr = "Provider = SQLOLEDB.1;Password=121231;Persist Security Info=True;User ID=sa;Initial Catalog=zydb;Data Source=wzsswz"
cn.ConnectionString = cnstr
cn.Open
Set cmd.ActiveConnection = cn
cmd.CommandText = "select * from company for XML auto"
strmResults.Open
cmd.Properties("Output Stream").Value = strmResults
cmd.Properties("xml root") = "root"
cmd.Execute , , adExecuteStream
strmResults.Position = 0
strmResults.SaveToFile App.Path & "/outfile.xml"
strmResults.Close
Set strmResults = Nothing
End Sub
2000的用select * from company for XML auto就可以了
Option Explicit
Dim conDB As New ADODB.Connection
Private Sub cmdGetData_Click()
' Get inventory data
Dim rsInventory As New ADODB.Recordset
Dim stmInventory As New ADODB.Stream
' set db connection
conDB.ConnectionString = ("Provider=SQLOLEDB.1;Server=Pinatubo;User ID=training; PWD=password;Initial Catalog=XMLTraining;")
conDB.Open
' set recordset
rsInventory.Open "tblInventory", conDB, adOpenDynamic, adLockOptimistic
rsInventory.Save stmInventory, adPersistXML
' Save ADO XML to file
stmInventory.SaveToFile App.Path & "/inventory.xml", adSaveCreateOverWrite
' dispaly xml file to UI
wbXML.Navigate App.Path & "/inventory.xml"
' close database connection
conDB.Close
End Sub
Private Sub cmdGetDetail_Click()
' Get product detail
Dim rsProductDetail As New ADODB.Recordset
Dim stmProduct As New ADODB.Stream
' Set connection string
conDB.ConnectionString = ("Provider=SQLOLEDB.1;Server=Pinatubo;User ID=training; PWD=password;Initial Catalog=XMLTraining;")
conDB.Open
' set recordset
rsProductDetail.Open "SELECT *, tblProductDetail.* FROM tblInventory INNER JOIN " & _
"tblProductDetail ON tblInventory.fldProductID = tblProductDetail." & _
"fldProductID", conDB, adOpenDynamic, adPersistXML
rsProductDetail.Save stmProduct, adPersistXML
' Save ADO XML file to disk
stmProduct.SaveToFile App.Path & "/ProductDetail.xml", adSaveCreateOverWrite
' Load xml document in UI
wbXML.Navigate App.Path & "/ProductDetail.xml"
' Close database connection string
conDB.Close
End Sub
在.NET中就方面多了
select * from table for xml auto
[责任编辑:editor]
问：如何终止一个被其它进程打开的Access文件？
解决方法：
Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Private Declare Function PostMessage Lib "user32" Alias "PostMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long
Private Declare Function GetClassName Lib "user32" Alias "GetClassNameA" (ByVal hwnd As Long, ByVal lpClassName As String, ByVal nMaxCount As Long) As Long
Private Declare Function ShowWindow Lib "user32" (ByVal hwnd As Long, ByVal nCmdShow As Long) As Long
Const SW_SHOWNORMAL = 1
Const WM_CLOSE = &H10
Const gcClassnameMSWord = "OpusApp"
Const gcClassnameMSExcel = "XLMAIN"
Const gcClassnameMSIExplorer = "IEFrame"
Const gcClassnameMSVBasic = "wndclass_desked_gsk"
Const gcClassnameNotePad = "Notepad"
Const gcClassnameMyVBApp = "ThunderForm"
Private Sub Form_Load()
Dim WinWnd As Long, Ret As String, RetVal As Long, lpClassName As String
'Search the window
WinWnd = FindWindow(vbNullString, "Microsoft Access")
If WinWnd = 0 Then MsgBox "Couldn't find the window ...": Exit Sub
'Show the window
ShowWindow WinWnd, SW_SHOWNORMAL
'Post a message to the window to close itself
PostMessage WinWnd, WM_CLOSE, 0&, 0&
End Sub
[责任编辑:editor]
