准则表达中的数据类型不匹配错误（ms Access）

Question

please figure out the error in my code.it show

DATA TYPE MISMATCH error IN CRITERIA EXPRESSION .

OleDbCommand cmd = new OleDbCommand("DELETE tbbill.*, tbgrid.* FROM tbbill INNER JOIN tbgrid ON tbbill.invoice = tbgrid.ginovice WHERE tbbill.invoice ='" + Convert.ToInt32(txtinvoice.Text) + "'", con);
cmd.ExecuteNonQuery();
cmd.Dispose();

Answer 1

It has to be

OleDbCommand cmd = new OleDbCommand(
                "DELETE tbbill.*, tbgrid.* 
                 FROM tbbill 
                 INNER JOIN tbgrid 
                    ON tbbill.invoice = tbgrid.ginovice 
                 WHERE tbbill.invoice = " + Convert.ToInt32(txtinvoice.Text) , con);

I have removed '' from the invoice

Whereas you should always use a parameterized SQL to prevent SQL Injections

OleDbCommand cmd = new OleDbCommand(
                "DELETE tbbill.*, tbgrid.* 
                 FROM tbbill 
                 INNER JOIN tbgrid 
                    ON tbbill.invoice = tbgrid.ginovice 
                 WHERE tbbill.invoice = @invoice", con);

cmd.Parameters.Add("@invoice", Convert.ToInt32(txtinvoice.Text) );  
cmd.ExecuteNonQuery();

Answer 2

Single quotes are for characters, if your invoice is numeric typed, you need to delete these quotes like;

tbbill.invoice = " + Convert.ToInt32(txtinvoice.Text) + ...

But don't use this way.

Always use parameterized queries . This kind of string concatenations are open for SQL Injection attacks.

And use using statement to dispose your command and connections automatically instead of calling Dispose method manually.

using(OleDbConnection con = new OleDbConnection(conString))
using(OleDbCommand cmd = con.CreateCommand())
{
    cmd.CommandText = "DELETE tbbill.*, tbgrid.* FROM tbbill INNER JOIN tbgrid ON tbbill.invoice = tbgrid.ginovice WHERE tbbill.invoice = @invoice";
    cmd.Parameters.Add("@invoice", OleDbType.Integer).Value = Convert.ToInt32(txtinvoice.Text);
    // I used OleDbType.Integer in my example. You should use proper OleDbType for your column.
    con.Open();
    cmd.ExecuteNonQuery();
}