如何在c＃中将加号之间的日期作为一个命令使用

Question

这是我的代码。 两者之间的日期有效，但是当我添加LEFT JOIN ，它会显示错误：

单词左边的语法错误

        cn.Open();
        SqlCommand cmd = cn.CreateCommand();
        cmd.CommandType = CommandType.Text;
        cmd.CommandText = "SELECT FirstName,LastName,Date,Time,Day from 
        Attendance where Sn=@Sn and ([Date] between @SD and @ED) left JOIN 
        EmployeeTable ON Attendance.EmployeeID = EmployeeTable.EmployeeID 
        Order by Attendance.AttendanceID";
        cmd.Parameters.Add(new SqlParameter("@Sn", txtSn.Text));
        cmd.Parameters.Add(new SqlParameter("@SD", DTPStart.Text));
        cmd.Parameters.Add(new SqlParameter("@ED", DTPEnd.Text));
        cmd.ExecuteNonQuery();
        DataTable dt = new DataTable();
        SqlDataAdapter sda = new SqlDataAdapter(cmd);
        sda.Fill(dt);
        dataGridView2.DataSource = dt;
        cn.Close();

Answer 1

您必须保持SQL语句的顺序。 首先是join ，然后where -clause。

更改

SELECT FirstName,LastName,Date,Time,Day from 
Attendance where Sn=@Sn and ([Date] between @SD and @ED) left JOIN 
EmployeeTable ON Attendance.EmployeeID = EmployeeTable.EmployeeID 
Order by Attendance.AttendanceID

至：

SELECT FirstName,LastName,Date,Time,Day from 
Attendance  left JOIN EmployeeTable ON Attendance.EmployeeID = EmployeeTable.EmployeeID 
where Attendance.Sn=@Sn and (Attendance.[Date] between @SD and @ED)
Order by Attendance.AttendanceID

https://technet.microsoft.com/en-us/library/ms190617(v=sql.105).aspx

Answer 2

这是因为你正在使用连接的地方。 它应该在之前和之后，在您处理多个表时尝试使用别名。 所以CommandText初始化将如下所示

cmd.CommandText = "SELECT b.FirstName,b.LastName,a.Date,a.Time,a.Day" +
                  " from Attendance a" +
                  " left JOIN EmployeeTable b ON a.EmployeeID = b.EmployeeID"  +
                  " where a.Sn=@Sn and (a.[Date] between @SD and @ED)" +
                  " Order by a.AttendanceID";

Answer 3

您得到的错误是因为您没有以正确的方式编写查询。 WHERE子句应始终位于JOIN语句之后。 还要确保在SQL查询中处理JOIN语句时应使用别名，以便更好地理解。

我已经编辑了你的代码，你可以用现有代码替换它：

cn.Open();
SqlCommand cmd = cn.CreateCommand();
cmd.CommandType = CommandType.Text;
cmd.CommandText = "SELECT et.FirstName,et.LastName,at.Date,at.Time,at.Day from 
Attendance at left JOIN 
EmployeeTable et ON at.EmployeeID = et.EmployeeID 
where at.Sn=@Sn and (at.[Date] between @SD and @ED)
Order by Attendance.AttendanceID";
cmd.Parameters.Add(new SqlParameter("@Sn", txtSn.Text));
cmd.Parameters.Add(new SqlParameter("@SD", DTPStart.Text));
cmd.Parameters.Add(new SqlParameter("@ED", DTPEnd.Text));
cmd.ExecuteNonQuery();
DataTable dt = new DataTable();
SqlDataAdapter sda = new SqlDataAdapter(cmd);
sda.Fill(dt);
dataGridView2.DataSource = dt;
cn.Close();