c# - How to use wildcards in SQL query with parameters

Question

Say I have a basic query, something like this:

 SELECT holiday_name
 FROM holiday
 WHERE holiday_name LIKE %Hallow%

This executes fine in my sql query pane and returns 'Halloween'. My problem occurs when I try to use parameters with with the wildcard '%' characters in my code.

SqlConnection Connection = null;
SqlCommand Command = null;

string ConnectionString = ConfigurationManager.ConnectionStrings["SQLdb"].ConnectionString;
string CommandText = "SELECT holiday_name "
                   + "FROM holiday "
                   + "WHERE holiday_name LIKE %@name%";
Connection = new SqlConnection(ConnectionString);

try
{
      Connection.Open();
      Command = new SqlCommand(CommandText, Connection);
      Command.Parameters.Add(new SqlParameter("name", HolidayTextBox.Text));
      var results = Command.ExecuteScalar();
}

catch (Exception ex)
{   
     //error stuff here       
}

finally
{
    Command.Dispose();
    Connection.Close();
}

This throws an incorrect syntax error. I've tried moving the '%' to my parameter like so

Command.Parameters.Add(new SqlParameter("%name%", HolidayTextBox.Text));

but then I receive an error saying I haven't declared the scalar variable '@name'. So, how do you properly format wildcard characters to be included with query parameters? Any help is appreciated!

Answer 1

First off, your SqlParameter name is @name not name.

Second, I would move your wildcards.

So it would look like this:

string CommandText = "SELECT holiday_name "
               + "FROM holiday "
               + "WHERE holiday_name LIKE @name;"
Connection = new SqlConnection(ConnectionString);

try
{
  var escapedForLike = HolidatyTextBox.Text; // see note below how to construct 
  string searchTerm = string.Format("%{0}%", escapedForLike);
  Connection.Open();
  Command = new SqlCommand(CommandText, Connection);
  Command.Parameters.Add(new SqlParameter("@name", searchTerm));
  var results = Command.ExecuteScalar();
}

Note that LIKE requires special care when passing parameters and you need to escape some characters Escaping special characters in a SQL LIKE statement using sql parameters.