How to group and count attribute data?

I suggest you to install Group Stats plugin. Here is a quick tutorial:

1. Search for the Group Stats icon
2. Select the layer in which you have the Codes
3. Select the attribute (in your case Code)
4. Click on Calculate

The Count will appear. If you go to preferences you should be able to select only Count avoiding the other parameters to be displayed (this is not my case...). Remember before click Save button you have to select the fields you want to add to your .csv: hold on Shift for do that. Here is a more advanced tutorial written by Anita Graser.

you could also use Qspatialite in QGIS. The SQL window is just as Mapinfo one. Up to you after to make your SQL request with a groupby command on the wanted column.

This was the best result on Google I could find, but the screenshot tutorial by G M is out of date and it took me a while to work out how to use the plugin.

1. Once installed, Load the Group Stats control panel from the "Vector" menu.
2. Select the layer of interest.
3. From the fields list, drag the field of interest into the "rows" box.
4. Now drag the same field into the "value" box.
5. In the fields list are also some functions, drag "count" into the "value" box (below the field you put in there).
6. Click "calculate" and a table will appear on the left.
7. You can sort by the count if you wish, click the column label.

How this helps other people.

With the new virtual layer you can now use SQL on any layer in QGIS, for example the airport Shapefile from the QGIS sample data:

To count the number of airports by USE type and compute the average elevation use:

The results are loaded as a new layer:

QGIS 3.10 comes with a "Statistics by categories" tool in the processing toolbox.

This is the result: