访问类型不匹配

Question

Having two tables:

MyTable1:
  id       AutoNumber
  typecode Text

MyTable2
  id      AutoNumber
  pid     Number
  freq    Number

using System.Data.OleDb;
namespace AccessSelect
{
    class Program
    {
        static void Main(string[] args)
        {
            var sql = @"select 'x' from mytable1 where typecode=@typeCode and EXISTS (
                        select 'x' from mytable2 where (freq=0 OR freq=@freq) and mytable1.id=mytable2.pid)";

            using (OleDbConnection conn = new OleDbConnection(@"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=gpi.mdb;Jet OLEDB:Database Password=???"))
            {
                conn.Open();
                OleDbCommand cmd = new OleDbCommand(sql, conn);

                cmd.Parameters.Add(new OleDbParameter("@typeCode", "KK3000"));
                cmd.Parameters.Add(new OleDbParameter("@freq", 50));

                var o = cmd.ExecuteScalar();
            }
        }
    }
}

I keep getting the exception 'Data type mismatch in criteria expression.'

If I change the SQL to contain the values:

select 'x' from mytable1 where typecode='KK3000' and EXISTS (
 select 'x' from mytable2 where (freq=0 OR freq=50) and  mytable1.id=mytable2.pid)

I don't get the error....

Any idea to what is wrong?

Answer 1

From MSDN :

The OLE DB .NET Provider does not support named parameters for passing parameters to an SQL statement or a stored procedure called by an OleDbCommand when CommandType is set to Text. In this case, the question mark (?) placeholder must be used. For example:

So change your query to:

select 'x' from mytable1 where typecode = ? 
     and EXISTS (select 'x' from mytable2 where (freq=0 OR freq = ?) and mytable1.id=mytable2.pid)

And you have to add parameters in the same order as they occur in query.

Answer 2

Changed it to:

static void Main(string[] args)
{
    var sql = @"select 'x' from mytable1 where typecode=@typeCode and EXISTS (
                select 'x' from mytable2 where (freq=0 OR freq=@freq) and mytable1.id=mytable2.pid)";

    using (OleDbConnection conn = new OleDbConnection(@"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=gpi.mdb;Jet OLEDB:Database Password=???"))
    {
        conn.Open();
        OleDbCommand cmd = new OleDbCommand(sql, conn);

        cmd.Parameters.Add(new OleDbParameter("@freq", 50));
        cmd.Parameters.Add(new OleDbParameter("@typeCode", "KK3000"));

        var o = cmd.ExecuteScalar();
    }
}

and now it seems to work... a bit strange though...