Here is free Windows program to automatically delete those missing musics. iTunes Missing Tracks Remover. Simply download it then unzip and run (no installation needed).

System requirement : iTunes 10 or later, Windows XP or 7.

You can also display exact duplicates, to do this hold Shift then click File -> Display Exact Duplicates. It will display songs with the same name, artist and album.

The next task is unchecking the songs that you want to keep because by default iTunes checks them all. Then select Edit -> Delete from menu.

Pretty straightforward isn’t it, but imagine if you have hundreds or thousand duplicates in your library, and you have to unchecking one by one ! or if you want to display duplicates which have same name, artist, album and time, iTunes couldn’t do that.

Automatically find and delete duplicates in iTunes

Let me introduce you iDeduper (http://www.ideduper.com) and for Mac, iMDeduper (http://www.imdeduper.com).  iDeduper is a software to delete duplicates in iTunes fast.

The first step is download it from the link above and then install and open it. Next click Search from menu.

As you can see, we can customize which tag to compared to find duplicates. Click Ok. It will search for duplicates based on criteria you set and display them.

Next click Auto Mark

We can select what method to automatically marking / checking the duplicates. There are by bitrate, time,  size, artwork, date added, rating, play count,  type and folder. And the most important feature is Mark all except one which will mark all but one song on each duplicate group. Select the method you want and click OK.

The last step is click Delete from menu. There is an option whether you want to also delete associated file. And done ! your iTunes library is clean from duplicates now!