VB实现数据库查询并显示

你就没打开数据库怎么就关闭了？
应该先连接数据库

Private Sub Command3_Click()
Dim cn As New ADODB.Connection
Dim rs As New ADODB.Recordset
Dim str As String
cn.Open("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=e:\DB\db1.mdb;Persist Security Info=False")'这里边是连接字符串，看你连接什么数据库

If Text3.Text = "" Then
str = "select * from 考勤信息表"
Else
str = "select *form 考勤信息表 where 姓名='" & Text3.Text & "'"
End If
rs.Open(str, cn, ADODB.CursorTypeEnum.adOpenKeyset,ADODB.LockTypeEnum.adLockOptimistic)Set DBGrid1.DataSource = rs
cn.close
rs=nothing
cn=nothing
End Sub

rs.Open也不对
res.Open

把 rs.Close 去掉