Question

我遇到了一个奇怪的问题我在sql数据库中有2个表所以我想编写一个查询，给出2个表数据的结果 2个表具有相同的列名，如

admission_number
student_name
student_class 我想以给定的图像 enter image description here 执行该查询执行查询后得到的数据将被加载到C＃
中的win-form编码的datagridview中我使用下面的代码来训练它，但它完全与我的问题无关，请帮助我。

 private void report()
    {
        dataGridView4.AutoResizeColumns();
        dataGridView4.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.AllCells;


        ConnectionStringSettings consettings = ConfigurationManager.ConnectionStrings["smssms"];
        string connectionString = consettings.ConnectionString;
        SqlConnection cn = new SqlConnection(connectionString);

        SqlCommand sqlcmd = new SqlCommand();
        SqlDataAdapter sda = new SqlDataAdapter();
        DataTable dt = new DataTable();

        cn.Open();
        //pass query 

        sqlcmd = new
SqlCommand(@"selectt.admission_number,t.student_name,t.student_class,e.admission_number,e.student_name,e.student_class
from tenthclass_marks as t,eighth_to_ninth_marks as e ", cn);
        sda = new SqlDataAdapter(sqlcmd);
        //Fill the data in the SQL Data Adapter
        sda.Fill(dt);
        //Bind it in the DataGrid View
        dataGridView4.DataSource = dt;
        cn.Close();

    }

Answer 1

您的查询：

select  t.admission_number,
        t.student_name,
        t.student_class,
        e.admission_number,
        e.student_name,
        e.student_class
from    tenthclass_marks as t,
        eighth_to_ninth_marks as e

正在生成两个表的Cartesian Product。也就是说tenthclass_marks中的每一行都与每一行eighth_to_ninth_marks组合在一起，所以如果每个表有5行，最后会有25行（5 x 5）。

您需要使用UNION ALL来合并结果：

SELECT  t.admission_number,
        t.student_name,
        t.student_class
FROM    tenthclass_marks AS t
UNION ALL
SELECT  e.admission_number,
        e.student_name,
        e.student_class
FROM    eighth_to_ninth_marks AS e;

对于你的c＃值，你也可以清理一下：

private void report()
{
    dataGridView4.AutoResizeColumns();
    dataGridView4.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.AllCells;
    string connectionString = ConfigurationManager.ConnectionStrings["smssms"].ConnectionString;
    string sql = @"SELECT   t.admission_number,
                            t.student_name,
                            t.student_class
                    FROM    tenthclass_marks AS t
                    UNION ALL
                    SELECT  e.admission_number,
                            e.student_name,
                            e.student_class
                    FROM    eighth_to_ninth_marks AS e;";

    DataTable dt = new DataTable();     
    using (var adapter = new SqlDataAdapter(sql, connectionString))
    {
        adapter.Fill(dt);
    }
    dataGridView4.DataSource = dt;
}

Answer 2

在两个表之间使用 UNION ALL

Select * from tenthclass_marks 
Union All 
Select * from eighth_to_ninth_marks

如何在c＃和Sql中只执行一次查询两个相同列的表到datagridview列

2 个答案: