title: How to merge 10 collections (with the same structure) into a single collection?
body: <p>I have 10 collections (with the names user_01, user_02, ... user_10). These 10 collections all have the same structure (I import from CSV file into MongoDB). Because the data of each CSV file is too big I have to split into 10 different files (data_01.csv, data_02.csv, ... data_10.csv) when importing into MongoDB (I put in 10 different collections as above, not a single collection).</p>
  <p>But now I need to merge these 10 collections into a single collection called &quot;user&quot; to query data. Is there any way to migrate data from these 10 collections into a single collection called &quot;user&quot;?</p>
  <p>The structure of each collection :</p>
  <pre><code>{
      &quot;_id&quot; : ObjectId(&quot;6119cac0fe31d614997b07f0&quot;),
      &quot;name&quot;: &quot;Robert&quot;
      &quot;address&quot; : &quot;36 rue Nationale, Paris, France&quot;,
      &quot;sex&quot; : &quot;female&quot;,
      &quot;age&quot; : 45,
      &quot;account_activated_date&quot; : 19990101
  }
  </code></pre>