How can I delete from database without the key?

I have a cart table that has cartId as the primary key, userId and itemId. I want to delete every row that has the id of a given user

Let's say this is my table:

I want to delete the information regarding user 5, so my table will look like this:

I have trid this SQL:

public static bool DeleteItemsFromCartByUserId(int userId) 
{
    string sql = string.Format("delete from [cart] where [userId] = {0}", userId);
    return Dbf.UpdateTable(sql) == 1;
}

public static int UpdateTable(string sql)
{
    OleDbConnection obj = Dbf.GenerateConnection();
    OleDbCommand cmd = new OleDbCommand(sql, obj);
    int value = cmd.ExecuteNonQuery();
    obj.Close();
    return value;
}

Every other delete sql that I wrote works perfectly fine - it returns true and deletes the information, but this one returns false and doesn't delete for some reason.

How can I do it if I don't have the cardId's?

OleDbCommand.ExecuteNonQuery returns the number of rows that were affected by the command. In your example, you are deleting two rows, but only checking if one row is affected, hence the FALSE return value.

A moderately better check would be:

return Dbf.UpdateTable(sql) > 0;

However you are still missing some best practices regarding SQL queries in C#, namely:

• Use of SQL parameters instead of formatting/concatenating SQL strings
• Disposing of connections and commands
• Proper error handling

You probably would have also seen this if you stored the result in a variable and checked it in the debugger rather than inlining the function call and the comparison in a return statement.