怎么用VB写代码判断数据库是不是已经打开

Dim c As New ADODB.Connection

Dim r As New ADODB.Recordset

Dim a As Long

Dim i As Long

On Error Resume Next

a = 0

c.Open C_Str

c.BeginTrans

If c.State = 1 Then

r.Open "select top 0 * from sfk", c, adOpenStatic, adLockOptimistic

If r.State = 1 Then

......

If c.State = 1 Then 这一句就是判断数据库是否成功连接

If r.State = 1 Then 这一句就是判断数据表sfk是否成功打开

1.c++连接连接access

程序代码:

using system.data

using system.data.oledb

..

string strconnection="provider=microsoft.jet.oledb.4.0"

strconnection+=@"data source=c:begaspnetnorthwind.mdb"

oledbconnection objconnection=new oledbconnection(strconnection)

..

objconnection.open()

objconnection.close()

2.c++连接sql server

程序代码:

using system.data

using system.data.sqlclient

..

string strconnection="user id=sapassword="

strconnection+="initial catalog=northwindserver=yoursqlserver"

strconnection+="connect timeout=30"

sqlconnection objconnection=new sqlconnection(strconnection)

..

objconnection.open()

objconnection.close()

3.c++连接mysql

程序代码:

using mysqldrivercs

// 建立数据库连接

mysqlconnection dbconn

dbconn = new mysqlconnection(new mysqlconnectionstring("localhost","mysql","root","",3306).asstring)

dbconn.open()

// 执行查询语句

mysqlcommand dbcomm

dbcomm = new mysqlcommand("select host,user from user",dbconn)

// 读取数据

mysqldatareader dbreader = dbcomm.executereaderex()

// 显示数据

try

{

while (dbreader.read())

{

console.writeline("host = {0} and user = {1}", dbreader.getstring(0),dbreader.getstring(1))

}

}

finally

{

dbreader.close()

dbconn.close()

}

//关闭数据库连接

dbconn.close()

4.c++连接ibm db2

程序代码：

oledbconnection1.open()

//打开数据库连接

oledbdataadapter1.fill(dataset1,"address")

//将得来的数据填入dataset

datagrid1.databind()

//绑定数据

oledbconnection1.close()

//关闭连接

//增加数据库数据

在web form上新增对应字段数量个数的textbox，及一个button，为该按键增加click响应事件代码如下：

this.oledbinsertcommand1.commandtext = "insertsintosaddress(name,

email, age, address) values

(’"+textbox1.text+"’,’"+textbox2.text+"’,’"+textbox3.text+"’,’"+textbox4.text+"’)"

oledbinsertcommand1.connection.open()

//打开连接

oledbinsertcommand1.executenonquery()

//执行该sql语句

oledbinsertcommand1.connection.close()

//关闭连接

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