So the difficulty of the first function which is to update the mysql database is to grab a google sheet table and return it as an array to make very long single insert statement INSERT INTO Table ( Column1, Column2 ) VALUES
( Value1, Value2 ), ( Value1, Value2 ), etc.
There's 5 custom functions in total to be written (get, put, summary, update, create). I can give you access to my test DB and google sheet where I already made the JDBC connection. So you can have a look first if you like.