Have you ever needed to merge multiple CSV files with millions of rows?  If you search online, you'll find how to do so either with Power Query in Excel, or through Unix cat or Windows copy, or even with some custom Python script.  However, all of these methods come with there own issues.

With Power Query you have to do a lot of up front setup with a custom source directory and setting custom column rules to be merged and later will need to clean up the duplicate headers that it will pull over into your merged sheet.  I won't attempt to explain how this works because I've never had to do so, but know you will have to be somewhat comfortable with advanced Excel skills to do this.  However, even if you know how to do this you will encounter the issue with a max row count of 1,048,576 rows that Excel 2007, 2010 and 2013 support.

With Unix cat or Windows copy it's as simple as a one line command:

Unix: cat *.csv > merged.csv

Windows: copy *.csv merged.csv

The problem with this solution is that you will be left with duplicate headers showing up throughout the merged.csv file.  It's even worse if your CSV files have inconsistent headers.  If this is the case you cannot just simply combine the files because then you will have the merged.csv file completely out of whack as you could imagine.

What's left to do is come up with your own custom Python script or even Unix awk to handle the most custom of needs, but who wants to do that?  What if you have no experience with programming and need a quick solution?

In comes Mighty Merge an online tool to quickly and easily merge multiple CSV files.  You simply drag and drop as many CSV files onto the page and press Merge.

Mighty Merge Demo

The whole process takes seconds to complete.  The most amazing thing about this tool is that no files are uploaded at all.  Everything happens locally in your browser safely and secure.  Mighty Merge auto-magically removes duplicate headers and auto-aligns all inconsistent headers.  So even if your CSV files have no columns in common, the final merged file will still line up all your columns perfectly.  As a bonus Mighty Merge will even join two CSV files horizontally based on a common column key.  Useful for when you have two CSV that are missing column information (e.g. joining a CSV file with product information, but perhaps missing a description column you have in another file).