title: How to merge two csv files in powershell with same headers and discard duplicate rows
body: <p>I am collecting performance counters from NetApp Performance Manager software (OPM). OPM saves 30 days worth of data in MySQL database. So i have to put two queries to retrieve the data:</p>
  
  <ol>
  <li>First Query on 30th of every month and save in csv file.</li>
  <li>Second Query on 1st of every month and save in csv file.</li>
  </ol>
  
  <p>Then merge the two csv files to get data if there are 31 days in a month.</p>
  
  <p>Both files look like below:</p>
  
  <pre><code>"Time","objid","cpuBusy","cifsOps","avgLatency"
  "2016:06:04 00:04","72","50.6196","2069.11","7622.1"
  "2016:06:04 00:09","72","30.2233","2075.94","7633.27"
  "2016:06:04 00:14","72","35.2559","1980.64","8352.17"
  </code></pre>
  
  <p>When i merge the two csv files with below code. I get duplicate rows with data from same data/time.</p>
  
  <pre><code>@(Import-Csv au2004npsa003-mm-business.csv) + @(Import-Csv au2004npsa003-nn-business.csv) | export-csv joined.csv -NoTypeInformation
  </code></pre>
  
  <p>How can i merge the two csv files without getting duplicate data?
  I have tried <code>select -unique</code> however, it gives just one row.</p>