code: function (database, table, callback) {
          var s = this,
              querier = s._querier;
          querier.connect();
          querier.selectKeyColumnUsage(database, table, function (err, data) {
              querier.disconnect();
              callback(err, s._parseTableKeyColumnUsageData(data));
          });
          return s;
      }
docs: Describe key column usage for a table.
  @param {string} database - Name of database.
  @param {string} table - Name of table.
  @param {function} callback - Callback when done.
  @returns {MysqlDescriber}