从 SQL Server 表中删除一行

Question

我正在尝试使用按钮事件从我的 SQL Server 数据库表中简单地删除一整行。到目前为止，我的任何尝试都没有成功。这就是我想要做的：

public static void deleteRow(string table, string columnName, string IDNumber)
{
    try
    {
    using (SqlConnection con = new SqlConnection(Global.connectionString))
    {
         con.Open();
         using (SqlCommand command = new SqlCommand("DELETE FROM " + table + " WHERE " + columnName + " = " + IDNumber, con))
         {
               command.ExecuteNonQuery();
         }
         con.Close();
    }
    }
    catch (SystemException ex)
       {
       MessageBox.Show(string.Format("An error occurred: {0}", ex.Message));
       }
    }
}

我一直收到错误：

System.Data.dll 中发生了“System.Data.SqlClient.SqlException”类型的第一次机会异常 发生错误：操作数类型冲突：文本与 int 不兼容

表中的所有列都是TEXT 类型。为什么我不能将 string 类型的函数参数与列进行比较以找到匹配项？ （然后删除该行？）

Answer 1

正如您所说，所有列名都是 TEXT 类型，因此，需要通过在 IDNumber 周围使用单引号将 IDNumber 用作文本.....

    public static void deleteRow(string table, string columnName, string IDNumber)
    {
    try
    {
    using (SqlConnection con = new SqlConnection(Global.connectionString))
    {
         con.Open();
         using (SqlCommand command = new SqlCommand("DELETE FROM " + table + " WHERE " + columnName + " = '" + IDNumber+"'", con))
         {
               command.ExecuteNonQuery();
         }
         con.Close();
    }
    }
    catch (SystemException ex)
       {
       MessageBox.Show(string.Format("An error occurred: {0}", ex.Message));
       }
    }
 }

Answer 2

IDNumber 应该是 int 而不是 string，或者如果它真的是 string，请添加引号。

更好的是，使用参数。

Answer 3

用参数试试

.....................
.....................

    using (SqlCommand command = new SqlCommand("DELETE FROM " + table + " WHERE " + columnName + " = " + @IDNumber, con))
             {
                   command.Paramter.Add("@IDNumber",IDNumber)
                   command.ExecuteNonQuery();
             }

.....................
.....................

using语句无需关闭连接

Answer 4

看起来 IDNumber 是一个字符串。它需要用单引号括起来。

"DELETE FROM " + table + " WHERE " + columnName + " = '" + IDNumber + "'"

Answer 5

您可以将“columnName”类型从TEXT 更改为VARCHAR(MAX). TEXT 列不能与"=" 一起使用。
see this topic

Answer 6

private void button4_Click(object sender, EventArgs e)
{
    String st = "DELETE FROM supplier WHERE supplier_id =" + textBox1.Text;

    SqlCommand sqlcom = new SqlCommand(st, myConnection);
    try
    {
        sqlcom.ExecuteNonQuery();
        MessageBox.Show("delete successful");
    }
    catch (SqlException ex)
    {
        MessageBox.Show(ex.Message);
    }
}



private void button6_Click(object sender, EventArgs e)
{
    String st = "SELECT * FROM suppliers";

    SqlCommand sqlcom = new SqlCommand(st, myConnection);
    try
    {
        sqlcom.ExecuteNonQuery();
        SqlDataReader reader = sqlcom.ExecuteReader();
        DataTable datatable = new DataTable();
        datatable.Load(reader);
        dataGridView1.DataSource = datatable;
    }
    catch (SqlException ex)
    {
        MessageBox.Show(ex.Message);
    }
}

Answer 7

如果您使用的是 MySql Wamp。此代码有效。

string con="SERVER=localhost; user id=root; password=; database=dbname";
public void delete()
{
try
{
MySqlConnection connect = new MySqlConnection(con);
MySqlDataAdapter da = new MySqlDataAdapter();
connect.Open();
da.DeleteCommand = new MySqlCommand("DELETE FROM table WHERE ID='" + ID.Text + "'", connect);
da.DeleteCommand.ExecuteNonQuery();

MessageBox.Show("Successfully Deleted");
}
catch(Exception e)
{
MessageBox.Show(e.Message);
}
}

Answer 8

private void DeleteProductButton_Click(object sender, EventArgs e)
{


    string ProductID = deleteProductButton.Text;
    if (string.IsNullOrEmpty(ProductID))
    {
        MessageBox.Show("Please enter valid ProductID");
        deleteProductButton.Focus();
    }
    try
    {
        string SelectDelete = "Delete from Products where ProductID=" + deleteProductButton.Text;
        SqlCommand command = new SqlCommand(SelectDelete, Conn);
        command.CommandType = CommandType.Text;
        command.CommandTimeout = 15;

        DialogResult comfirmDelete = MessageBox.Show("Are you sure you want to delete this record?");
        if (comfirmDelete == DialogResult.No)
        {
            return;
        }
    }
    catch (Exception Ex)
    {
        MessageBox.Show(Ex.Message);

    }
}