Question

我正在编写桌面应用程序。在一个表单中，我从数据库表中获取最大日期并填入文本框（tbdate）。现在我有另一个文本框（tbvouch），它将获得最大的vouchernumber + 1，其中date = tbdate。用户也可以自己输入日期。

现在如果该日期出现在表格中，那么它必须选择最大值vouchernumber +1。另外，它默认将凭证号码设为5001。

以上逻辑我正在放置文本框（tbvouch）的ENTER事件。我的代码是

  private void tbvouch_Enter(object sender, EventArgs e)
    {

        DateTime d = Convert.ToDateTime(tbdate.Text);
        int vcnum;
        SqlConnection c = new SqlConnection();
        c.ConnectionString = "Data Source=.\\SQLEXPRESS;AttachDbFilename='D:\\Documents\\Visual Studio 2008\\Projects\\Accounts\\Accounts\\Database1.mdf';Integrated Security=True;User Instance=True";
        c.Open();
        string q = "select max(vc_number) from lgr where date = '"+d+"' ";
        SqlCommand cmd = new SqlCommand(q, c);
        SqlDataReader rd = cmd.ExecuteReader();
        try
        {
            if (rd.Read())
            {
                int val = rd.GetInt32(0);
                if (val != 0)
                {
                    vcnum = val + 1;
                    tbvouch.Text = vcnum.ToString();
                }
            }
        }
        catch (Exception ex)
        {
            tbvouch.Text = "05001";
        }
    }

Answer 1

  private void tbvouch_Enter(object sender, EventArgs e)
    {

        DateTime d = Convert.ToDateTime(tbdate.Text);
        int vcnum;
        SqlConnection c = new SqlConnection();
        c.ConnectionString = "Data Source=.\\SQLEXPRESS;AttachDbFilename='D:\\Documents\\Visual Studio 2008\\Projects\\Accounts\\Accounts\\Database1.mdf';Integrated Security=True;User Instance=True";
        c.Open();

        string q = "IF EXISTS(SELECT 1 FROM lgr WHERE date = @date) 
                    BEGIN 
                         select max(vc_number)+1 from lgr where date = @date 
                    END 
                    ELSE 
                    BEGIN SELECT 05001 END";
       using (var cmd = new SqlCommand(q, con))
       {
        cmd.CommandType = CommandType.Text;

        cmd.Parameters.Add("@date", SqlDbType.DateTime).Value = d;

        vcum = (int)cmd.ExecuteScalar();
        }
}

如何获取日期等于某个日期的任何列的最大值

1 个答案: