How to Specify sadd’s Target Database in php

  node.js, question

For example, I want to insert data into library number 1 instead of the default library number 0
I know in the command line is to use select 1 and then saddxxxx yyy.
But how to write code in php

<?  php
 $redis = new Redis();
 echo $redis->get('test');
 $redis->sAdd('s', 5);
 $redis->sAdd('s', 4);
 $redis->sAdd('s', 2);
 $redis->sAdd('s', 1);
 $redis->sAdd('s', 3);
 var_dump($redis->sort('s'));  // 1,2,3,4,5