NO -- First let's decide what the full situation is.

What version are you using? If MySQL 5.7, consider going to utf8mb4 so that you can handle Emoji and all of Chinese. If 5.5 or 5.6, that is also possible, but you might run into some problems.

http://mysql.rjweb.org/doc.php/charcoll#fixes_for_various_cases

Case 1: The columns are currently CHARACTER SET latin1 and contain only latin1-encoded text. Then do this for each table:

ALTER TABLE t CONVERT TO CHARACTER SET utf8;

Case 2: The columns are currently CHARACTER SET latin1 but you have utf8-encoded characters in them. This leads to Mojibake or the silent "double encoding". The fix needs a pair of alters for each column:

Case 3 (double encoding): Then, and only then, this is called for:

UPDATE tbl SET col = CONVERT(BINARY(CONVERT(col USING latin1)) USING utf8mb4);

More discussion

CHARACTER SET latin1, but have utf8 bytes in it; leave bytes alone while fixing charset: First, lets assume you have this declaration for tbl.col:

col VARCHAR(111) CHARACTER SET latin1 NOT NULL

Then to convert the column without changing the bytes:

ALTER TABLE tbl MODIFY COLUMN col VARBINARY(111) NOT NULL;
ALTER TABLE tbl MODIFY COLUMN col VARCHAR(111) CHARACTER SET utf8mb4 NOT NULL;

Note: If you start with TEXT, use BLOB as the intermediate definition. (This is the "2-step ALTER, as discussed elsewhere.) (Be sure to keep the other specifications the same - VARCHAR, NOT NULL, etc.)

Which case??

In order to determine which case you have, please provide a small sample of the current data via:

 SELECT HEX(col), col FROM t WHERE ...

Example: If the col has é, and the HEX is E9 -- that's latin1. If the Hex is C3A9, it's utf8 improperly stored into latin1. Hex of C383C2A9 would indicate "double encoding".

Generate ALTERs

A tip on how to generate the ALTERs can be found here . (It is not exactly what you need, but close.)

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);

This is a common problem, so here's a relatively thorough illustration.

For non-unicode strings (i.e. those without u prefix like u'\xc4pple'), one must decode from the native encoding (iso8859-1/latin1, unless modified with the enigmatic sys.setdefaultencoding function) to unicode, then encode to a character set that can display the characters you wish, in this case I'd recommend UTF-8.

First, here is a handy utility function that'll help illuminate the patterns of Python 2.7 string and unicode:

>>> def tell_me_about(s): return (type(s), s)

A plain string

>>> v = "\xC4pple" # iso-8859-1 aka latin1 encoded string

>>> tell_me_about(v)
(<type 'str'>, '\xc4pple')

>>> v
'\xc4pple'        # representation in memory

>>> print v
?pple             # map the iso-8859-1 in-memory to iso-8859-1 chars
                  # note that '\xc4' has no representation in iso-8859-1, 
                  # so is printed as "?".

Decoding a iso8859-1 string - convert plain string to unicode

>>> uv = v.decode("iso-8859-1")
>>> uv
u'\xc4pple'       # decoding iso-8859-1 becomes unicode, in memory

>>> tell_me_about(uv)
(<type 'unicode'>, u'\xc4pple')

>>> print v.decode("iso-8859-1")
Äpple             # convert unicode to the default character set
                  # (utf-8, based on sys.stdout.encoding)

>>> v.decode('iso-8859-1') == u'\xc4pple'
True              # one could have just used a unicode representation 
                  # from the start

A little more illustration — with “Ä”

>>> u"Ä" == u"\xc4"
True              # the native unicode char and escaped versions are the same

>>> "Ä" == u"\xc4"  
False             # the native unicode char is '\xc3\x84' in latin1

>>> "Ä".decode('utf8') == u"\xc4"
True              # one can decode the string to get unicode

>>> "Ä" == "\xc4"
False             # the native character and the escaped string are
                  # of course not equal ('\xc3\x84' != '\xc4').

Encoding to UTF

>>> u8 = v.decode("iso-8859-1").encode("utf-8")
>>> u8
'\xc3\x84pple'    # convert iso-8859-1 to unicode to utf-8

>>> tell_me_about(u8)
(<type 'str'>, '\xc3\x84pple')

>>> u16 = v.decode('iso-8859-1').encode('utf-16')
>>> tell_me_about(u16)
(<type 'str'>, '\xff\xfe\xc4\x00p\x00p\x00l\x00e\x00')

>>> tell_me_about(u8.decode('utf8'))
(<type 'unicode'>, u'\xc4pple')

>>> tell_me_about(u16.decode('utf16'))
(<type 'unicode'>, u'\xc4pple')

Relationship between unicode and UTF and latin1

>>> print u8
Äpple             # printing utf-8 - because of the encoding we now know
                  # how to print the characters

>>> print u8.decode('utf-8') # printing unicode
Äpple

>>> print u16     # printing 'bytes' of u16
���pple

>>> print u16.decode('utf16')
Äpple             # printing unicode

>>> v == u8
False             # v is a iso8859-1 string; u8 is a utf-8 string

>>> v.decode('iso8859-1') == u8
False             # v.decode(...) returns unicode

>>> u8.decode('utf-8') == v.decode('latin1') == u16.decode('utf-16')
True              # all decode to the same unicode memory representation
                  # (latin1 is iso-8859-1)

Unicode Exceptions

 >>> u8.encode('iso8859-1')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 0:
  ordinal not in range(128)

>>> u16.encode('iso8859-1')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'ascii' codec can't decode byte 0xff in position 0:
  ordinal not in range(128)

>>> v.encode('iso8859-1')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc4 in position 0:
  ordinal not in range(128)

One would get around these by converting from the specific encoding (latin-1, utf8, utf16) to unicode e.g. u8.decode('utf8').encode('latin1').

So perhaps one could draw the following principles and generalizations:

• a type str is a set of bytes, which may have one of a number of encodings such as Latin-1, UTF-8, and UTF-16
• a type unicode is a set of bytes that can be converted to any number of encodings, most commonly UTF-8 and latin-1 (iso8859-1)
• the print command has its own logic for encoding, set to sys.stdout.encoding and defaulting to UTF-8
• One must decode a str to unicode before converting to another encoding.

Of course, all of this changes in Python 3.x.

Hope that is illuminating.

Further reading

• Characters vs. Bytes, by Tim Bray.

And the very illustrative rants by Armin Ronacher:

• The Updated Guide to Unicode on Python (July 2, 2013)
• More About Unicode in Python 2 and 3 (January 5, 2014)
• UCS vs UTF-8 as Internal String Encoding (January 9, 2014)
• Everything you did not want to know about Unicode in Python 3 (May 12, 2014)

I have found a half-part way in this. This is not what you want / need, but might help others in the right direction...

# First read the file
txt = open("file_name", "r", encoding="latin-1") # r = read, w = write & a = append
items = txt.readlines()
txt.close()

# and write the changes to file
output = open("file_name", "w", encoding="utf-8")
for string_fin in items:
    if "é" in string_fin:
        string_fin = string_fin.replace("é", "é")

    if "ë" in string_fin:
        string_fin = string_fin.replace("ë", "ë")

    # this works if not to much needs changing...

    output.write(string_fin)

output.close();

*note for detection

I managed to solve it by running updates on text fields like this:

UPDATE table SET title = CONVERT(CONVERT(CONVERT(title USING latin1) USING binary) USING UTF8)

Unicode is certainly difficult, and the UTF-8 encoding has a couple of inconvenient properties. However, UTF-8 has become the de-facto standard encoding on the web, surpassing ASCII, Latin-1, UCS-2 and UTF-16. Just use UTF-8 everywhere.

The most important reason why you should support Unicode is that you shouldn't make unnecessary assumptions about user input. I have no idea what your domain is, but things like Hebrew usernames, a blog post about China, a comment with Emoji, or simply well styled text – like “this” – should be possible… Oh, those were typographically correct quotation marks (“” rather than ""), en-wide dashes, and an ellipsis, which are characters that are common in English text, but not supported by ASCII or Latin-1. So not supporting other scripts isn't just a big f*ck you to other cultures, but sticking to Latin-1 doesn't even allow you to write proper English.

The notion that Unicode only allows “bad characters” is wrong. Yes, text is really complicated, and Unicode won't hide that from you. Your boss may be thinking about composed characters, where one base codepoint such as a is modified by subsequent codepoints that e.g. represent diacritics to form one visual character such as á. This doesn't really get into your way when trying to do searches if you do some kind of normalization. For example, you could store all text in the NFC form which collapses such compositions into their precomposed form if one is available. When doing searching, you could also strip all composing characters from the text, but this may substantially change their meaning in some languages.

Unicode also adds a lot of unprintable characters – but even ASCII has loads of them. Will you handle a NUL in the middle of a string? How about 0x1C, a “File Separator”? I've never seen half of those. Latin-1 adds a soft hyphen that indicates word break opportunities, but is otherwise invisible. Does that also break your full-text search? In other words, even ASCII and Latin-1 allow you to completely break your input if you assume it's all just printable text!