c#如何获取数据库中某个表中的其中一个字段的值

一段代码：直接粘贴过去就可以了
private string get(string tablname, string column, string text, string selcolumn)//tablname数据库表名 column选择的列名 selcolumn 限制的列名 text 限制的内容
{
using(SqlConnection conn = new SqlConnection(source))//source是连接字符串
{
try
{
conn.Open();
string cmdtext = @"select top 1 " + selcolumn + " from " + tablname + " where " + column + " = '" + text + "'";
SqlCommand cmd = new SqlCommand(cmdtext, conn);
return Convert.ToString(cmd.ExecuteScalar());
}
catch(Exception ex)
{
return "something error!! ";
}
}
}

//数据库连接字符串
private string str1 = "Provider=SQLOLEDB;Server=(loca