Mysql installation conflict with mariadb

Error :
Renaming removed key_buffer and myisam-recover options (if present)

mysql_upgrade: Got error: 1524: Plugin 'unix_socket' is not loaded while connecting to the MySQL server

Upgrade process encountered error and will not continue.
mysql_upgrade failed with exit status 11

dpkg: error processing package mysql-server-5.7 (--configure):subprocess installed post-installation script returned error exit status 1

Errors were encountered while processing:mysql-server-5.7

Solution :
If you have installed MariaDB and then you have removed it to install mysql. This can be the cause of this issue. If you try to purge all old config filess and set everything up from scratch then it should work. 
Take Back up your important data before doing it.

# sudo apt purge mysql-client-5.7 mysql-client-core-5.7 mysql-common mysql-server-5.7 mysql-server-core-5.7 mysql-server
# sudo apt update 
# sudo apt dist-upgrade && sudo apt autoremove && sudo apt -f install
# sudo apt install mysql-server

Odoo - Remove Manage Databases link from Login page

Odoo - Remove Powered by Odoo Text from Login page

Edit file addons/web/views/webclient_templates.xml
sudo nano /opt/odoo/addons/web/views/webclient_templates.xml

Remove or Comment text "Manage Databases" and "Powered by Odoo".

Now you tried to restart the odoo server but you are not able to see your changes on the browser.

Here you need to load the web module because you ahve changed content in the file of web module. Without loading web module, you will not be able to see your changes. Restarting Odoo does not load the web module.

sudo -S su postgres -c "./odoo-bin start --update=web"

--update=all loads all modules but we need to reload only web module to see the changes. Now changes will be visible.

mysql - select query denied error

select command denied to user ''@'' for table ''

Solution :

You are getting this error because you are logged into the mysql user account where Select_priv is set as N for the user.

If you are able to modify your own privileges that is really good (Generally this can't be done because of security) otherwise you need to login with super user and need to set this privilege as Y.

Run this query :

update user set Select_priv = 'Y' where User = 'username';

Changes will not take effect after running this query. You will have to flush privileges.

Run Query :

FLUSH PRIVILEGES;

After flushing privileges, if still you face denied error for select query, Log out from mysql, Log in again with same user and running select query again.
You will not get the error.

If you get same denied error for Insert, Update and Delete queries, you need to set them as Y using same method.

Restarting mysql does the job but every time you do not have command line access to restart it that's why you need to flush privileges.