Incorrect String Value in MySQL db - mysql

Question

I am running a webapp on Ubuntu 16.04.4.
The stack is as follows
Python 3.5.2
MySQL 5.7.22
Flask
Flask-SQLAlchemy
The webapp has a feature for admins to upload some text using a xlsx. file which is read with openpyxl inside the webapp. However while saving I am getting errors like:
sqlalchemy.exc.OperationalError: (_mysql_exceptions.OperationalError) (1366, "Incorrect string value: '\\xC4\\x9B nep...'
In the beginning I was able to delete the characters which were making troubles (e.g. zero width whitespace). But now I am not able to do it anymore like this.
Reading a bit on the internet I think it could be that my db is not using utf8mb4. Could someone lead me to update my db and all its tables? Because I do not know anything about SQL and stuff.
As the webapp is used in production I do not like to try tutorials which are outdated.

Answer 1

Seems to work now. I did following steps:
Started the mysql cli with:
mysql -u root -p
Logged in using the root pw.
Checked the default parameters using
show variables like "%character%";
which gave me:
+--------------------------+----------------------------+
| Variable_name | Value |
+--------------------------+----------------------------+
| character_set_client | utf8 |
| character_set_connection | utf8 |
| character_set_database | latin1 |
| character_set_filesystem | binary |
| character_set_results | utf8 |
| character_set_server | latin1 |
| character_set_system | utf8 |
| character_sets_dir | /usr/share/mysql/charsets/ |
+--------------------------+----------------------------+
and
show variables like "%collation%";
which gave me
+----------------------+-------------------+
| Variable_name | Value |
+----------------------+-------------------+
| collation_connection | utf8_general_ci |
| collation_database | latin1_swedish_ci |
| collation_server | latin1_swedish_ci |
+----------------------+-------------------+
So I edited /etc/mysql/my.cnf
I added:
[client]
default-character-set = utf8mb4
[mysql]
default-character-set = utf8mb4
[mysqld]
character-set-server = utf8mb4
collation-server = utf8mb4_unicode_ci
Restarting mysql (sudo service mysql restart) and running the same commands as above now gave me
+--------------------------+----------------------------+
| Variable_name | Value |
+--------------------------+----------------------------+
| character_set_client | utf8mb4 |
| character_set_connection | utf8mb4 |
| character_set_database | utf8mb4 |
| character_set_filesystem | binary |
| character_set_results | utf8mb4 |
| character_set_server | utf8mb4 |
| character_set_system | utf8 |
| character_sets_dir | /usr/share/mysql/charsets/ |
+--------------------------+----------------------------+
and
+----------------------+--------------------+
| Variable_name | Value |
+----------------------+--------------------+
| collation_connection | utf8mb4_general_ci |
| collation_database | utf8mb4_unicode_ci |
| collation_server | utf8mb4_unicode_ci |
+----------------------+--------------------+
So I looked up the table settings using
SHOW TABLE STATUS FROM databasename;
They still used stuff like latin1_swedish_ci
I used following to change the database setting:
ALTER DATABASE databasename CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
and following for each table:
use databasename;
ALTER TABLE assessments CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
Looking up again the table settings showed that latin1_swedish_ci was now changed to utf8mb4_unicode_ci
Then I changed the sqlalchemy connection url to use ?encoding=utf8mb4 at the end.
Restarted mysql again and the webapp. Since then it's working properly.