仅当Image_ID1
和Image_ID2
不是时,这些方法才会给出结果null
。如果其中一个或两个都为空,则显示错误。除了仅返回偶数计数外,还将跳过奇数计数。示例,列Image_ID1=1,3,null
和Image_ID2=2,4,6
。它必须显示1,2,3,4,6
值,但显示1,2,3,4
导致该null
值的值。我该如何解决这些问题?
private void BindGrid()
{
MySqlConnection con = new MySqlConnection(constr);
MySqlCommand cmd = new MySqlCommand("SELECT * FROM images where Image_ID in (" + String.Join(",", getImage_ID()) + ")", con);
MySqlDataAdapter da = new MySqlDataAdapter(cmd);
DataTable dt = new DataTable();
da.Fill(dt);
gvImages.DataSource = dt;
gvImages.DataBind();
}
private List<int> getImage_ID()
{
List<int> i = new List<int>();
MySqlConnection con = new MySqlConnection(constr);
con.Open();
string query = "Select Image_ID1, Image_ID2 from register where students_ID='" + getStudents_ID() + "'AND Image_ID1 IS NOT NULL AND Image_ID2 IS NOT NULL";
MySqlCommand cmd = new MySqlCommand(query);
cmd.Connection = con;
MySqlDataReader reader = cmd.ExecuteReader();
foreach (DbDataRecord s in reader)
{
i.Add(s.GetInt32(0));
i.Add(s.GetInt32(1));
}
return i;
}
我建议使用一个查询/方法:
string sql = @"
SELECT img.* FROM
(
SELECT i.* FROM Images i
INNER JOIN register r
ON i.Image_ID = r.Image_ID1
WHERE r.students_ID = @studentsID
UNION ALL
SELECT i.* FROM Images i
INNER JOIN register r
ON i.Image_ID = r.Image_ID2
WHERE r.students_ID = @studentsID
) img
";
MySqlCommand cmd = new MySqlCommand(sql , con);
cmd.Parameters.Add("@studentsID", MySqlDbType.Int32).Value = getStudents_ID();
MySqlDataAdapter da = new MySqlDataAdapter(cmd);
DataTable dt = new DataTable();
da.Fill(dt);
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