title: Grafana merge data from Prometheus exporters
body: <p>I am scraping data from 2 Prometheus exporters (node_exporter and push_gateway) which I want to merge in a Grafana table.</p>
  <p>The query for push_gateway returns something similar to:</p>
  <pre><code>sum(input_files) by (exported_instance)
  
  exported_instance                   Value
  srv0000189014                       139
  srv0000189016                       314
  </code></pre>
  <p>The one from node_exporter has those 2 above and some extra data:</p>
  <pre><code>sum(time() - node_boot_time_seconds{source=&quot;node_exporter&quot;}) by (srv_instance)
  
  srv_instance                        Value
  srv0000189014                       59251
  srv0000189016                       2874194
  srv0000226683                       2874318
  srv0000189015                       2876153
  srv0000227715                       59269
  srv0000188188                       62992
  srv0000226685                       2873569
  srv0000188191                       3000257
  srv0000227713                       59392
  srv0000189013                       60968
  </code></pre>
  <p>I've tried to apply a merge transfrom but it doesn't work as expected:</p>
  <pre><code>exported_instance           srv_instance                Value #A        Value #B
  srv0000189016               srv0000227713               314             59850
  srv0000189016               srv0000188188               314             63450
  srv0000189016               srv0000226685               314             2874027
  srv0000189016               srv0000188191               314             3000715
  srv0000189016               srv0000227715               314             59727
  srv0000189016               srv0000189014               314             59709
  srv0000189016               srv0000189013               314             61426
  srv0000189016               srv0000226683               314             2874776
  srv0000189016               srv0000189016               314             2874652
  srv0000189016               srv0000189015               314             2876611
  srv0000189014                                           139
  </code></pre>
  <p>I would like the value <code>314</code> to be assigned only to <code>srv0000189016</code>, <code>139</code> to <code>srv0000189014</code> on the <code>Value #A</code> column and for the rest of the rows to not be displayed anything if there is no value.</p>
  <p>The entire <code>exported_instance</code> column can be removed.</p>