used wrong mysql connection encoding - need to convert data

Question

I have a Mysql database with all tables collated as 'utf8_unicode_ci'. Also all data I wrote to the Database with php was encoded in utf8. But I forgot to set the mysql connection encoding to utf8, so it probably defaulted to ISO-8859.

For a long time this was not a problem. Although special characters where displayed wrong in Tools like phpMyAdmin, the data was correct when loading it into my php application, as long as I kept using the wrong connection encoding.

But now I need to use my database from another application, that (correctly) does not use ISO-8859 as connection encoding and gets broken special characters.

Now I want to convert my database so I can use the right connection encoding.

I already tried this: mysql wrong connection encoding

But I does not help for me. The closest I got to a solution was 'ut8_decode(utf8_decode($data))'. But this breaks fields that start with a special character.

Additional Information:

So what might happen is the following:

1. My application sends some utf8 Data to the database.

2. Mysql gets the data but thinks (due to the connection encoding) that it is not utf8, and converts it, to fit for the 'utf8_unicode_ci' collation.

3. When my php application reads the data from the database mysql seems to undo the previous conversion so everything looks fine again from my php app.