尝试从数据库中删除行时“条件表达式中的数据类型不匹配”

Question

    OleDbCommand system = new OleDbCommand();
    system.CommandType = CommandType.Text;
    system.CommandText = "DELETE FROM Student WHERE(ID= '" + 
                          txtStudentIDnumber.Text + "')";
    system.Connection = mydatabase;

    mydatabase.Open();
    system.ExecuteNonQuery();
    dataGridView1.Update();

    this.tableAdapterManager.UpdateAll(csharrpfinalprojectDataSet);
    mydatabase.Close();

    MessageBox.Show("Student Record Deleted.", "deleting record...");

Answer 1

In your command text you need to remove single quotes (') around the txtStudentIDnumber.Text as it appears ID is of type integer and you are passing it as string. Following should fix the error.

system.CommandText = "DELETE FROM Student WHERE(ID= " + txtStudentIDnumber.Text + ")";

EDIT: With respect to @mdb comments, you should always use Parameters in your query so that you can avoid SQL Injection . Consider the following:

OleDbCommand system = new OleDbCommand();
system.CommandType = CommandType.Text;
system.CommandText = "DELETE FROM Student WHERE ID = ?";
OleDbParameter parameter = new OleDbParameter("ID", txtStudentIDnumber.Text);
system.Parameters.Add(parameter);
system.Connection = mydatabase;

mydatabase.Open();
system.ExecuteNonQuery();
dataGridView1.Update();

Answer 2

OleDbCommand system = new OleDbCommand();
system.CommandType = CommandType.Text;
system.CommandText = "DELETE FROM Student WHERE ID=@ID";
system.Parameters.AddWithValue("@ID", txtStudentIDnumber.Text);
system.Connection = mydatabase;

mydatabase.Open();
system.ExecuteNonQuery();
dataGridView1.Update();

this.tableAdapterManager.UpdateAll(csharrpfinalprojectDataSet);
mydatabase.Close();

MessageBox.Show("Student Record Deleted.", "deleting record...");

Answer 3

What will happen when user input for txtStudentIDNumber is,

1 or 1=1

In that case hardcoded SQL string will be,

DELETE FROM Student WHERE(ID=1 or 1=1)

So prefer parameterized sql statement instead of hard-coded string.

using(OleDbConnection cn=new OleDbConnection(cnStr))
 {
  using(OleDbCommand cmd=new OleDbCommand())
   {
    cmd.CommandText="DELETE FROM Student WHERE ID=@ID";
    cmd.Connection=cn;
    cmd.Parameters.Add("@ID",SqlDbType.Int).Value=txtStudentIDnumber.Text;
    cn.Open();
    cmd.ExecuteNonQuery();
    cn.Close();
   }
 }