使用 C# 在 MS 访问数据库中查找最大数字

Question

How to find the largest number in a particular column of MS access table? I'm using C#.

I'm not able to make the logic for this. I was doing this:

int i, lastID;
int y = 0;
int lastRow = DS.Tables[0].Rows.Count;
for (i = 0; i > -1; i++)
{
    i = Convert.ToInt32(DS.Tables[0].Rows[i]["id"].ToString());
    lastID = (y > i) ? y : i;
    if (i > lastRow)
    {
        lastID++;
        empIdLabel.Text = lastID.ToString();
    }
}

I'm fussed !!!!

Answer 1

Barring an obvious reason why not, you should use SQL: SELECT MAX(id) FROM. . . SELECT MAX(id) FROM. . . .

You can do this with an OLEDB connection:

OleDbConnection connection = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;data source=blahblah.mdb"));
connection.Open();
OleDbCommand maxCommand = new OleDbCommand("SELECT max(id) from TABLENAME", connection);
Int32 max = (Int32)maxCommand.ExecuteScalar();

Note that I'm on a Linux machine, so I haven't tested the above, but it should be pretty close from what I remember of C#.

Answer 2

 String cs = @"Provider=Microsoft.ACE.OLEDB.12.0;Data    
 Source=databasepath\databasename.mdb"; 
 OleDbConnection con = new OleDbConnection(cs);
 con.Open();
 OleDbCommand com = new OleDbCommand("select Max(id) as ID from tablename",
 con);
 com.CommandType = CommandType.Text;
 OleDbDataReader r = com.ExecuteReader();
 r.Read();
 if (r["ID"].ToString() != "")
           {
               temp = int.Parse(r["ID"].ToString()) + 1;
           }
 else
           {
                temp = 1;
           }
 textBox1.Text = temp.ToString();
 r.Close();
 con.Close();

Answer 3

you can use SQL for this purpose

select max(id) from tablename

Answer 4

It is recomended to do it in query rather than in code.

The query could be

Select Max(ColName) From TableName;