C# 如果数据库sum命令中没有行，则返回错误

将字符串值转换为int时，如果数据库中没有数据，则会引发错误

try {

        SqlCommand cmdc = new SqlCommand("SELECT SUM(Credited_amount) FROM IMS_Credit_Dir WHERE Credit_comp_id=1 AND Crdt_typ_id=1", con);
        string companya_credit_amount = null, comapnyb_credit_amount = null;
        con.Open();
        SqlDataReader drc = cmdc.ExecuteReader();

        if (drc.HasRows)
        {

            while (drc.Read())
            {
                companya_credit_amount = drc[0].ToString();
            }
            drc.Close();
            con.Close();
        }
        SqlCommand cmdcp = new SqlCommand("SELECT SUM(Credited_amount) FROM IMS_Credit_Dir WHERE Credit_comp_id=2 AND Crdt_typ_id=1", con);
        con.Open();
        SqlDataReader drcp = cmdcp.ExecuteReader();
        if (drcp.HasRows)
        {

            while (drcp.Read())
            {
                companyb_credit_amount = drcp[0].ToString();
            }
            drcp.Close();
            con.Close();
        }
        if (!Page.IsPostBack)
        {
            int companyA = 0,companyB=0;
            if (companya_credit_amount != "") { companyA = Convert.ToInt32(credit_amount.ToString()); }
            if (companyb_credit_amount != ""){ companyB = Convert.ToInt32(companyb_credit_amount); }
            int total = (companyA+companyB);
            count_total_lbl.Text = "Rs." + " " + total.ToString();
            count_comapnya_lbl.Text = "Rs." + " " + companya_credit_amount.ToString();
            count_companyb_lbl.Text ="Rs."+" "+ companyb_credit_amount.ToString();
        }
    }
    catch(Exception ex) { Label2.Text = ex.ToString(); }

如果有值，则其工作正常。但当数据库中没有值时，则会出现错误消息

System.FormatException:输入字符串的格式不正确

用于检查空值

创建并销毁在使用块中实现

IDisposable

的所有类型实例。这可确保始终释放连接并清理资源

不要跨类使用连接。在需要时创建它们，然后处置它们。Sql Server将处理连接池

直接获取本机类型，而不是等效的字符串！请参见数据读取器上对字符串的更改，而不是

ToString

您应该重构它以使用

SqlParameter

，并使检索语句成为泛型语句，或者在一个sql调用中获取两个总和值

如果（！Page.IsPostBack）语句中有

if（！Page.IsPostBack）

语句，如果是回发，则此代码中的任何代码都不会执行任何操作，然后在页面顶部进行检查，如果是回发，则不执行sql语句。否则代码会无缘无故地进行（可能）昂贵的sql调用

---

试着替换这个

SELECT SUM(Credited_amount) 

与

在转换贷记金额值时，也会发现一个令人困惑的代码

if (companya_credit_amount != "") { companyA = Convert.ToInt32(credit_amount.ToString()); }
                                                         ---------^^^^^
if (companyb_credit_amount != ""){ companyB = Convert.ToInt32(companyb_credit_amount); }

---

我不知道您的业务需求，但我认为应该使用

公司信用额
而不是
公司信用额
来显示
公司信用额
变量的价值，对吗？
您应该做两件事：

字符串companya_credit_amount=“”，comapnyb_credit_amount=“”

在将值分配给这些字符串变量之前，应检查db null，如下所示：

while (drc.Read())
{
companya_credit_amount = (drc[0] != DbNull.Value) ? drc[0].ToString() :    "" ;
}


相似地

    while (drcp.Read())
    {
       companyb_credit_amount = (drcp[0] != DbNull.Value) ? drcp[0].ToString() : "";
    }

试试看。
您需要将信用卡金额初始化为空，并检查db值是否为空，如下所示：

    try {
            companya_credit_amount = string.Empty;
            companyb_credit_amount = string.Empty;
            SqlCommand cmdc = new SqlCommand("SELECT SUM(Credited_amount) FROM IMS_Credit_Dir WHERE Credit_comp_id=1 AND Crdt_typ_id=1", con);
        string companya_credit_amount = null, comapnyb_credit_amount = null;
        con.Open();
        SqlDataReader drc = cmd

c.ExecuteReader();

    if (drc.HasRows)
    {

        while (drc.Read())
        {
            companya_credit_amount = drcp.IsDBNull(0)?string.Empty:Convert.ToString(drcp[0]);
        }
        drc.Close();
        con.Close();
    }
    SqlCommand cmdcp = new SqlCommand("SELECT SUM(Credited_amount) FROM IMS_Credit_Dir WHERE Credit_comp_id=2 AND Crdt_typ_id=1", con);
    con.Open();
    SqlDataReader drcp = cmdcp.ExecuteReader();
    if (drcp.HasRows)
    {

        while (drcp.Read())
        {
            companyb_credit_amount = drcp.IsDBNull(0)?string.Empty:Convert.ToString(drcp[0]);
        }
        drcp.Close();
        con.Close();
    }
    if (!Page.IsPostBack)
    {
        int companyA = 0,companyB=0;
        if (companya_credit_amount != "") { companyA = Convert.ToInt32(credit_amount.ToString()); }
        if (companyb_credit_amount != ""){ companyB = Convert.ToInt32(companyb_credit_amount); }
        int total = (companyA+companyB);
        count_total_lbl.Text = "Rs." + " " + total.ToString();
        count_comapnya_lbl.Text = "Rs." + " " + companya_credit_amount.ToString();
        count_companyb_lbl.Text ="Rs."+" "+ companyb_credit_amount.ToString();
    }
}
catch(Exception ex) { Label2.Text = ex.ToString(); }

哪一行引发异常？在转换为所需的数据类型之前，您需要检查所有可空列上的空值。为什么不将companya\u credit\u amount和companyb\u credit\u amount初始化为“0”而不是null？int total=（companya+companyb）//这里我得到了这条线上的错误你确定你得到了那条线上的错误吗？我非常怀疑这一行是否会给您带来格式异常，您确定这不是上面的Convert.ToInt32行吗？while（drc.Read（））{companya_credit_amount=drc.IsDBNull（0）？“0”：drc.GetString（0）；//error line}drc.Close（）；con.Close（）；无法将类型为“System.Int32”的对象强制转换为类型为“System.String”@ManoharKumar-您阅读了我的答案吗？不要使用字符串，因为您正在使用数字（整数）。使用本机类型（数字），而不是字符串。在bullet#4和我提供的代码中都有。@ManoharKumar-一个错误，
GetInt
应该是
GetInt32
，上面的代码已经更新。错误已经消失，但在标签中看不到值。输出为0。当我有一些价值的时候DB@ManoharKumar-直接在SSMS中运行查询并查看输出。如果按原样使用上述代码，标签将填充。我无法猜测您的版本现在是什么样子，但您必须逐步完成并调试代码。可能是您放错了
或未选中
Read（）
（以推进数据读取器）。是，我想显示金额的总和。特定公司的
    while (drcp.Read())
    {
       companyb_credit_amount = (drcp[0] != DbNull.Value) ? drcp[0].ToString() : "";
    }

    try {
            companya_credit_amount = string.Empty;
            companyb_credit_amount = string.Empty;
            SqlCommand cmdc = new SqlCommand("SELECT SUM(Credited_amount) FROM IMS_Credit_Dir WHERE Credit_comp_id=1 AND Crdt_typ_id=1", con);
        string companya_credit_amount = null, comapnyb_credit_amount = null;
        con.Open();
        SqlDataReader drc = cmd

c.ExecuteReader();

    if (drc.HasRows)
    {

        while (drc.Read())
        {
            companya_credit_amount = drcp.IsDBNull(0)?string.Empty:Convert.ToString(drcp[0]);
        }
        drc.Close();
        con.Close();
    }
    SqlCommand cmdcp = new SqlCommand("SELECT SUM(Credited_amount) FROM IMS_Credit_Dir WHERE Credit_comp_id=2 AND Crdt_typ_id=1", con);
    con.Open();
    SqlDataReader drcp = cmdcp.ExecuteReader();
    if (drcp.HasRows)
    {

        while (drcp.Read())
        {
            companyb_credit_amount = drcp.IsDBNull(0)?string.Empty:Convert.ToString(drcp[0]);
        }
        drcp.Close();
        con.Close();
    }
    if (!Page.IsPostBack)
    {
        int companyA = 0,companyB=0;
        if (companya_credit_amount != "") { companyA = Convert.ToInt32(credit_amount.ToString()); }
        if (companyb_credit_amount != ""){ companyB = Convert.ToInt32(companyb_credit_amount); }
        int total = (companyA+companyB);
        count_total_lbl.Text = "Rs." + " " + total.ToString();
        count_comapnya_lbl.Text = "Rs." + " " + companya_credit_amount.ToString();
        count_companyb_lbl.Text ="Rs."+" "+ companyb_credit_amount.ToString();
    }
}
catch(Exception ex) { Label2.Text = ex.ToString(); }