text: 
  const TABLE = 'user_environment_variable';
  const INDEX = 'user_environment_variable_site_name_idx';
  
  exports.up = function(db, callback) {
    db.addIndex(TABLE, INDEX, ['siteId', 'name'], true, callback);
  };
  
  exports.down = function(db, callback) {
    db.removeIndex(TABLE, INDEX, callback);
  };
  