C# 数据库的基本操作（sqlserver）

一、首先是与sqlserver的基本操作

连接字符在配置文件中是这样写的
[html]
<connectionStrings>
    <add name="ConnStr" connectionString="data source=xp-ba785745002d;database=databaseonline;Uid=sa;pwd=sasa"/>
</connectionStrings>

基本操作类如下：
[csharp]
public class SQLHelper
{
    private SqlConnection sqlCon = null;
    private SqlCommand cmd = null;
    private SqlDataReader sdr = null;
    public SQLHelper()
    {
        sqlCon = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnStr"].ConnectionString);
    }
/// <summary>
/// 打开数据库连接
/// </summary>
/// <returns></returns>
    private SqlConnection GetCon()
    {
        if (sqlCon.State==ConnectionState.Closed)
        {
          sqlCon.Open();
        }
        return sqlCon;
    }
    /// <summary>
    /// 执行不带参数的增删改sql语句或存储过程
    /// </summary>
    /// <param name="cmdText">增删改sql语句或存储过程</param>
    /// <param name="ct">命令类型</param>
    /// <returns></returns>
    public int ExecuteNonQuery(string cmdText, CommandType ct)
    {
        int rex;
        try
        {
        SqlCommand sqlcom = new SqlCommand(cmdText,GetCon());
        sqlcom.CommandType = ct;
        rex =sqlcom.ExecuteNonQuery();
        }
        catch (Exception ex)
        {

            throw ex;
        }
        finally
        {
            if (sqlCon.State==ConnectionState.Open)
            {
               sqlCon.Close();
            }
        }
        return rex;
    }
    /// <summary>
    /// 执行带参数的增删改SQL语句或存储过程
    /// </summary>
    /// <param name="cmdText">增删改SQL语句或存储过程</param>
    /// <param name="ct">命令类型</param>
    /// <returns></returns>
    public int ExecuteNonQuery(string cmdText, SqlParameter[] paras, CommandType ct)
    {
        int res;
        using (cmd = new SqlCommand(cmdText, GetCon()))
        {
            cmd.CommandType = ct;
            cmd.Parameters.AddRange(paras);
            res = cmd.ExecuteNonQuery();
        }
        return res;
    }
    /// <summary>
    /// 执行带参数的查询SQL语句或存储过程
    /// </summary>
    /// <param name="cmdText">查询SQL语句或存储过程</param>
    /// <param name="paras">参数集合</param>
    /// <param name="ct">命令类型</param>
    /// <returns></returns>
    public DataTable ExecuteQuery(string cmdText, SqlParameter[] paras, CommandType ct)
    {
        DataTable dt = new DataTable();
        cmd = new SqlCommand(cmdText,GetCon());
        cmd.CommandType = ct;
        cmd.Parameters.AddRange(paras);
        using (sdr = cmd.ExecuteReader(CommandBehavior.CloseConnection))
        {
            dt.Load(sdr);
        }
        return dt;
    }
    /// <summary>
    /// 执行不带参数的查询SQL语句或存储过程
    /// </summary>
    /// <param name="cmdText">查询SQL语句或存储过程</param>
    /// <param name="ct">命令类型</param>
    /// <returns></returns>
    public DataTable ExecuteQuery(string cmdText, CommandType ct)
    {
        DataTable dt = new DataTable();
        cmd = new SqlCommand(cmdText, GetCon());
        cmd.CommandType = ct;
        using (sdr = cmd.ExecuteReader(CommandBehavior.CloseConnection))
        {
            dt.Load(sdr);
        }
        return dt;
    }
}
下面是两中调用方法：
[csharp]
public int logincheck(string admin, string pwd)
{

    SqlParameter[] paras = new SqlParameter[] {
    new SqlParameter("@AdminName",admin),
    new

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