Convert all Rails table column collation and character set

character_set_and_collation.rb

#!/usr/bin/env ruby

# Put this file in the root of your Rails project,
# then run it to output the SQL needed to change all
# your tables and columns to the same character set 
# and collation.
#
# > ruby character_set_and_collation.rb

DATABASE      = ''
CHARACTER_SET = 'utf8'
COLLATION     = 'utf8_general_ci'

schema = File.open('db/schema.rb', 'r').read
rows = schema.split("\n")

table_name = nil
rows.each do |row|
  if row =~ /create_table/
    table_name = row.match(/create_table "(.+)"/)[1]
    puts "ALTER TABLE `#{DATABASE}`.`#{table_name}` DEFAULT CHARACTER SET #{CHARACTER_SET} COLLATE #{COLLATION};"
  elsif row =~ /t\.string/
    field_name = row.match(/"(.+)"/)[1]
    puts "ALTER TABLE `#{DATABASE}`.`#{table_name}` CHANGE COLUMN `#{field_name}` `#{field_name}` CHARACTER SET #{CHARACTER_SET} COLLATE #{COLLATION};"
  elsif row =~ /t\.text/
    field_name = row.match(/"(.+)"/)[1]
    puts "ALTER TABLE `#{DATABASE}`.`#{table_name}` CHANGE COLUMN `#{field_name}` `#{field_name}` CHARACTER SET #{CHARACTER_SET} COLLATE #{COLLATION};"
  end
end

CONVERT TO CHARACTER SET is great but MySQL warns against using it if the existing columns are latin1.

From https://dev.mysql.com/doc/refman/8.0/en/alter-table.html

The CONVERT TO operation converts column values between the original and named character sets. This is not what you want if you have a column in one character set (like latin1) but the stored values actually use some other, incompatible character set (like utf8mb4).