Select查询偶数和奇数个数

Question

只有当 Image_ID1 和 Image_ID2 都不是 null 时，这些方法才会给出结果。如果其中之一或两者都为空，则显示错误。除此之外 returns 只有偶数计数，奇数计数被跳过。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，但显示 1,2,3,4 值是 null 值的原因。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;
    }

Answer 1

我建议使用单个 query/method:

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);

Answer 2

而不是 getImage_ID() 方法中的 foreachloop 尝试下面提到的代码

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")));

}

Answer 3

问题出在您的 SQL

"'AND Image_ID1 IS NOT NULL AND Image_ID2 IS NOT NULL"

应该是

"'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));

Select查询偶数和奇数个数

Select query even and odd value count

c#

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