You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: db_open.m
    path of file: ./repos/spm/external/fieldtrip/fileio/private
    
    the code of the file until where you have to start completion: function db_open(user, password, server, port, database)

% DB_OPEN opens the connection to the database
%
% Use as
%    db_open
%    db_open(user, password, server, port, database)

    
function db_open(user, password, server, port, database)

% DB_OPEN opens the connection to the database
%
% Use as
%    db_open
%    db_open(user, password, server, port, database)
%    db_open('mysql://<user>:<password>@<host>:<port>')

% Copyright (C) 2007, Robert Oostenveld
%
% $Log: db_open.m,v $
% Revision 1.2  2007/11/27 14:38:49  roboos
% added query "use database"
%
% Revision 1.1  2007/11/07 10:50:46  roboos
% created helper functions for easy access to a MySQL database table using a structure for representing the data
%

% persistent variables should be defined at the beginning of the function
persistent prev_filename

switch nargin
  case 0
    % use the default settings and combine them in a string of the form mysql://<user>:<password>@<host>:<port>
    user     = 'fieldtrip';
    password = 'fieldtrip';
    server   = 'odin';
    port     = 3306;
    filename = sprintf('mysql://<%s>:<%s>@<%s>:<%d>', user, password, server, port);
  case 1
    % the database settings are specified as mysql://<user>:<password>@<host>:<port>
    filename = user;
    [user, password, server, port] = filetype_check_uri(filename);
  case 3
    % the port was not specified, combine the settings in a string of the form mysql://<user>:<password>@<host>
    filename = sprintf('mysql://<%s>:<%s>@<%s>', user, password, server);
  case 4
    % combine the settings in a string of the form mysql://<user>:<password>@<host>:<port>
    filename = sprintf('mysql://<%s>:<%s>@<%s>:<%d>', user, password, server, port);
  case 5
    % combine the settings in a string of the form mysql://<user>:<password>@<host>:<port>
    filename = sprintf('mysql://<%s>:<%s>@<%s>:<%d>/<%s>', user, password, server, port, database);
  otherwise
    ft_error('incorrect input arguments');
end