How to fix double-encoded UTF8 characters (in an utf-8 table)

The following MySQL function will return the correct utf8 string after double-encoding:

CONVERT(CAST(CONVERT(field USING latin1) AS BINARY) USING utf8)

It can be used with an UPDATE statement to correct the fields:

UPDATE tablename SET    field = CONVERT(CAST(CONVERT(field USING latin1) AS BINARY) USING utf8);

The above answer worked for some of my data, but resulted in a lot of NULL columns after running. My thought is if the conversion wasn't successful it returns null. To avoid that, I added a small check.

UPDATE    tblSET    col =    CASE        WHEN CONVERT(CAST(CONVERT(col USING latin1) AS BINARY) USING utf8) IS NULL THEN col        ELSE CONVERT(CAST(CONVERT(col USING latin1) AS BINARY) USING utf8)    END

I meet this issue too, here a solution for Oracle:

update tablename t set t.colname = convert(t.colname, 'WE8ISO8859P1', 'UTF8') where t.colname like '%Ã%'

And another one for Java:

public static String fixDoubleEncoded(String text) {    final Pattern pattern = Pattern.compile("^.*Ã[^0-9a-zA-Z\\ \t].*$");    try {        while (pattern.matcher(text).matches())            text = new String(text.getBytes("iso-8859-1"), "utf-8");    }    catch (UnsupportedEncodingException e) {        e.printStackTrace();    }    return text;}