title: How to set up kdb RDB to only subscribe to certain tables in tickerplant
body: <p>I want to set up 2 RDB instances using the same script where one instance subscribes to 2 tables and the other instance subscribes to a separate table in the tickerplant. I am trying to manipulate .u.sub but with no success</p>
  <pre><code>if[system&quot;p&quot;=RDB_INSTANCE_1;
     .u.rep .(hopen `$&quot;:&quot;,.u.x 0)&quot;({.u.sub[x;`]} each `trade`quote;`.u `i`L)&quot;;
  ];
  </code></pre>
  <pre><code>if[system&quot;p&quot;=RDB_INSTANCE_2;
     .u.rep .(hopen `$&quot;:&quot;,.u.x 0)&quot;(.u.sub[`aggTradeStats;`];`.u `i`L)&quot;;
  ];
  </code></pre>
  <p>or</p>
  <pre><code>   ?[system&quot;p&quot;=RDB_INSTANCE_1;..u.rep .(hopen `$&quot;:&quot;,.u.x 0)&quot;({.u.sub[x;`]} each `trade`quote;`.u `i`L)&quot;; .u.rep .(hopen `$&quot;:&quot;,.u.x 0)&quot;(.u.sub[`aggTradeStats;`];`.u `i`L)&quot;];
  </code></pre>
  <p>Any idea how I can achieve this?</p>