Question

我想从一个表中检索员工的姓名，并从另一个表中检索他们的请假申请的详细信息。将员工与其报告老板区分开的条件是manager_ID列。 employee_ID作为每个用户的manager_ID列的值提供。导演在这个领域是空的。现在，我使用以下查询在gridview中填充了这些数据。

SqlConnection conn = new SqlConnection(connectionstring);
SqlCommand cmd = new SqlCommand("select distinct Employee.emp_name,Leave.leave_ID,Leave.leave_type,Leave.reason,Leave.el_start_date,Leave.el_end_date,Leave.total_days,Leave.status from Employee CROSS JOIN Leave where Employee.manager_ID='" + lbl_empid.Text + "' AND Leave.status='" + lbl_status.Text + "'", conn);
cmd.CommandType = CommandType.Text;

using (conn)
{
    conn.Open();
    rdr = cmd.ExecuteReader();
    while (rdr.Read())
    {
        dr = dt.NewRow();
        dr["Leave No."] = rdr["leave_ID"].ToString();
        dr["Requested By"] = rdr["emp_name"].ToString();
        dr["Type of Leave"] = rdr["leave_type"].ToString();
        dr["Reason"] = rdr["reason"].ToString();
        dr["Starting"] = rdr["el_start_date"].ToString();
        dr["Ending"] = rdr["el_end_date"].ToString();
        dr["No. of Days"] = rdr["total_days"].ToString();
        dr["Status"] = rdr["status"].ToString();

        dt.Rows.Add(dr);
        dt.AcceptChanges();
    }

    gv_pending_requests.DataSource = dt;
    gv_pending_requests.DataBind();
    conn.Close();
}

在调试时，gridview将填充而不会出现错误。它显示了由登录管理员管理的员工，可以。只有那些员工＆＃39;检索并显示所需的行。但数据以奇怪的方式重复。在输出中使用替换名称重复相同的行。我粗略模仿了我在gridview中得到的输出，因为我不允许发布图像。输出通过重复显示具有相同管理器的所有用户的数据。虽然实际上我只是从Avneesh的帐户提出这些请求，而不是ravi：

Lv. No.  Employee Name     LeaveType                  Reason           Starting Date
2        Avneesh           Earned, Casual            Personal          17/11/2014   
2        Ravi              Earned, Casual            Personal          17/11/2014 
5        Avneesh           Earned, Half-Pay          Conference        17/11/2014   
5        Ravi              Earned, Half-Pay          Conference        17/11/2014

请指出我在查询中做错了什么。我尝试在子查询中使用自联接，但它显示错误： - {＆＃34; System.Data.SqlClient.SqlException（0x80131904）：关键字附近的语法不正确＆＃39;其中＆＃39;＆＃34 ;}。查询是：

SqlCommand cmd = new SqlCommand("select distinct Employee.emp_name,Leave.leave_ID,Leave.leave_type,Leave.reason,Leave.el_start_date,Leave.el_end_date,Leave.total_days,Leave.status from Employee CROSS JOIN Leave where Employee.manager_ID=(select e.emp_ID,m.emp_ID from Employee e INNER JOIN Employee m where e.mgr_ID=m.emp_ID) AND Leave.status='" + lbl_status.Text + "'", conn);

现在，我该如何解决这种重复问题？请帮忙。我正在使用Visual Studio 2013和sql server 2014。编辑：以下是与此查询有关的两个表。

   CREATE TABLE [dbo].[Employee](
[emp_ID] [numeric](18, 0) IDENTITY(1,1) NOT NULL,
[username] [nvarchar](50) NOT NULL,
[emp_name] [nvarchar](max) NOT NULL,
[password] [nvarchar](max) NOT NULL,
[pay_roll_num] [nvarchar](max) NOT NULL,
[designation] [nvarchar](max) NOT NULL,
[leaves_taken] [nvarchar](max) NOT NULL,
[primary_address] [nvarchar](max) NOT NULL,
[primary_phone] [nvarchar](max) NOT NULL,
[email_ID] [nvarchar](max) NOT NULL,
[manager_ID] [nvarchar](max) NOT NULL,
     CONSTRAINT [PK_Employee] PRIMARY KEY CLUSTERED (   [username] ASC)WITH (PAD_INDEX = OFF,  
     STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]


    CREATE TABLE [dbo].[Leave](
[leave_ID] [numeric](18, 0) IDENTITY(1,1) NOT NULL,
[username] [nvarchar](50) NOT NULL,
[reason] [nvarchar](max) NOT NULL,
[addrs_onLeave] [nvarchar](max) NOT NULL,
[phone_onLeave] [nvarchar](max) NOT NULL,
[alternate_email] [nvarchar](max) NULL,
[leave_type] [nvarchar](max) NOT NULL,
[earned_leave] [nvarchar](max) NULL,
[el_start_date] [nvarchar](max) NULL,
[el_end_date] [nvarchar](max) NULL,
[halfpay_leave] [nvarchar](max) NULL,
[hl_start_date] [nvarchar](max) NULL,
[hl_end_date] [nvarchar](max) NULL,
[commuted_leave] [nvarchar](max) NULL,
[com_startdate] [nvarchar](max) NULL,
[com_end_date] [nvarchar](max) NULL,
[casual_leave] [nvarchar](max) NULL,
[cl_start_date] [nvarchar](max) NULL,
[cl_end_date] [nvarchar](max) NULL,
[rh_leave] [nvarchar](max) NULL,
[rh_start_date] [nvarchar](max) NULL,
[rh_end_date] [nvarchar](max) NULL,
[total_days] [nvarchar](max) NOT NULL,
[status] [nvarchar](max) NOT NULL,
[leave_apply_date] [nvarchar](max) NOT NULL,
    CONSTRAINT [PK_Leave] PRIMARY KEY CLUSTERED (   [leave_ID] ASC)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]

Answer 1

我同意CROSS JOIN是问题。

当该表或查询集有多行时，很少需要对表或查询集进行CROSS JOIN，从而创建一个笛卡尔积。另一方面，我经常将CROSS JOIN连接到其中包含SINGLE行的表或查询，但这样做不会增加结果集中的行数，从而不会重复行。

概念化何时将CROSS JOIN用于多行表或集合的一个很好的示例是需要过帐借方和贷记（双重记账）的批处理过程。您可以加入包含两行的查询，其中一行包含＆＃39; DEBIT＆＃39;，另一行＆＃39; CREDIT＆＃39;，这样做只会使批次中的所有行加倍。一半是作为DEBIT发布的，另一半是作为CREDIT发布的。

Answer 2

解决了！谢谢大家建议摆脱交叉连接。这是正确的查询，以防其他人可能需要它。

 SqlCommand cmd = new SqlCommand("select distinct leave_ID,username,leave_type,reason,
 el_start_date,el_end_date,total_days,status from Leave where username IN 
 (select username from Employee where manager_ID='" + lbl_empid.Text + "')
 AND Leave.status='" + lbl_deny.Text + "'", conn);

在gridview中将查询结果加入不同但重复的数据中

2 个答案: