Question

我正在尝试从数据中获取单个字段。（我正在用主键搜索，所以我应该得到0或1个答案）。请帮忙。我查询的表有一个条目，用户=某人，输入到几列，ans列有“一个好的答案”

代码：

Dim reader As SqlDataReader
Dim par As SqlParameter
Dim result As String

Dim sqlconn As SqlConnection
sqlconn = New SqlConnection("....")
sqlconn.Open()

Dim sqlcmd As SqlCommand
sqlcmd = New SqlCommand("Select Ans From Test Where User = @auser", sqlconn)

par = New SqlParameter
par.ParameterName = "auser"
par.Value = Textbox1.Text

sqlcmd.Parameters.Add(par)

reader = sqlcmd.ExecuteReader()

result = reader.GetString(0)

''//output to label
label1.Text = result

Answer 1

您需要先读取数据读取器，然后将其放在第一行。

所以而不是

reader = sqlcmd.ExecuteReader()    
result = reader.GetString(0)

您可以像这样插入Read（）方法：

reader = sqlcmd.ExecuteReader()    
if reader.Read() then '' <<<<< newly inserted code
    result = reader.GetString(0)
end if

Answer 2

''// using statement will guarantee the object is closed and disposed
''// even if an exception occurs
Using sqlconn As New SqlConnection("...."), _
      sqlcmd As  New SqlCommand("Select Ans From Test Where User = @auser", sqlconn)

    ''// you can create, add, and set the value for a parameter all on one line
    sqlcmd.Parameters.Add("@auser", SqlDbType.VarChar, 50).Value = Textbox1.Text

    ''//wait as long as possible to open the connection
    sqlconn.Open() 

    ''// if you're only getting the first column of the first row, use execute scalar
    label1.Text = CString(sqlcmd.ExecuteScalar())

End Using

SQL从vb中的表读取数据

代码：

2 个答案: