title: How to search in multiple Indexes in SOLR
body: <p>Currently i have three cores in solr and my requirement is to search over all core.Cores have similarities in their fields name like below,</p>
  <blockquote>
  <p>core1: schema: field A, field B, field C, field D, field E</p>
  <p>core2: schema: field A, field M, field N, field D</p>
  <p>core3: schema: field X,
  field Y, field B, field N</p>
  <p><em>( Don't go for the above patterns in fields, those are to explain that there are few</em>
  <em>similarities and dissimilarities in fields in these 3 cores.</em>)</p>
  </blockquote>
  <p>Now to search all over these cores altogether, i have implemented below two solutions:</p>
  <blockquote>
  <ol>
  <li><p>I have kept all three cores same as it is and created one core and put one schema that is union of all three schema from all three cores,
  and in solr config put the parameter, &quot;shards&quot; with the address of
  three cores. Basically this newly created core is not having any
  indexed data and when we are searching this core it is actually
  redirecting it to three cores and clubbing the results and returning
  it i guess.
  <a href="https://stackoverflow.com/questions/39450164/how-to-search-multiple-solr-core">How to Search Multiple SOLR Core?</a></p>
  </li>
  <li><p>Put all core in one core. creating one schema on that core that is union of all three schema from all three cores and making all fields
  optional(required=false), accomplished in a single index with an
  additional field to select what type to search.
  <a href="https://wiki.apache.org/solr/MultipleIndexes" rel="nofollow noreferrer">https://wiki.apache.org/solr/MultipleIndexes</a></p>
  </li>
  </ol>
  </blockquote>
  <p>Now both these solutions work perfectly, but i am not sure which one to adopt. So looking for a clear pros and cons(i know few but not very clear) to select the better.</p>
  <p><strong>Also want to know is there will be any difference in score calculation or relevance at the time of searching for these above two approaches if we keep all setting same in all places for these two.</strong></p>