选择查询偶数和奇数值计数
本文关键字:选择 查询 | 更新日期: 2023-09-27 18:13:31
这些方法只有在Image_ID1
和Image_ID2
都不是null
时才给出结果。如果其中一个或两个为空,则显示错误。此外,它只返回偶数值计数,奇数值计数被跳过。例如,列Image_ID1=1,3,null
和Image_ID2=2,4,6
。它必须显示1,2,3,4,6
值,但由于null
值,它显示1,2,3,4
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;
}
我建议使用单个查询/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);
代替getImage_ID()方法中的foreachloop试试下面提到的代码
while (reader.Read())
{
if (!reader.IsDBNull(reader.GetOrdinal("Image_ID1")))
i.Add(reader.GetInt32(reader.GetOrdinal("Image_ID1")));
if (!reader.IsDBNull(reader.GetOrdinal("Image_ID2")))
i.Add(reader.GetInt32(reader.GetOrdinal("Image_ID2")));
}
问题是SQL
中的条件"'AND Image_ID1 IS NOT NULL AND Image_ID2 IS NOT NULL"
应该改成
"'AND (Image_ID1 IS NOT NULL OR Image_ID2 IS NOT NULL)"
那么foreach
正文应该是
if (!s.IsDBNull(0)) i.Add(s.GetInt32(0));
if (!s.IsDBNull(1)) i.Add(s.GetInt32(1));