themactep

a collection of miscellaneous projects of Paul Philippov

Database Useful Tips

How to quickly secure MySQL after installation

$ /usr/bin/mysql_secure_installation

How to force MySQL server to use unicode

$ sudo -s
# echo "[mysqld]
collation_server=utf8_unicode_ci
character_set_server=utf8
skip-character-set-client-handshake
" > /etc/mysql/conf.d/utf8.cnf
# /etc/init.d/mysql restart
# exit

How to limit access to MySQL to a sub-network

$ sudo -s
# iptables -A INPUT -p tcp -s 192.168.0.0/32 --dport 3306 -j ACCEPT
# iptables -A INPUT -p tcp --dport 3306 -j DROP
# exit

How to dump remote MySQL database to a local file

$ ssh <user@server> "mysqldump --user=<dbuser> --password=<dbpassword> \
  <dbname> | bzip2 --stdout --force" | bzip2 --decompress --stdout \
  > <dbname>_$(date +%Y-%m-%d_%H:%M:%S).sql

to dump data only:

$ ssh <user@server> "mysqldump --user=<dbuser> --password=<dbpassword> \
  --compact --no-create-info --complete-insert \
  <dbname> | bzip2 --stdout --force" | bzip2 --decompress --stdout \
  > <dbname>_$(date +%Y-%m-%d_%H:%M:%S).sql

How to change MySQL server root password on Debian

$ sudo dpkg-reconfigure mysql-server

How to add a constraint to an existing SQLite table

CREATE UNIQUE INDEX table_i ON table(id, type);

How to disable ONLY_FULL_GROUP_BY mode in MySQL 5.7

$ sudo -s
# echo '[mysqld]
sql_mode = "STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION"
' > /etc/mysql/conf.d/fullgroup.cnf
# /etc/init.d/mysql restart
# exit

How to add a user in MySQL

GRANT ALL PRIVILEGES ON <database>.* TO '<user>'@'localhost' IDENTIFIED BY '<password>';
FLUSH PRIVILEGES;

How to convert DB to full Unicode in an older Rails project

Adjust encoding in database.yml as following:

  encoding: utf8mb4
  collation: utf8mb4_polish_ci

Create and run the following migration:

class ConvertToFullUnicode < ActiveRecord::Migration[5.0]
  def change
    config = Rails.configuration.database_configuration
    db_name = config[Rails.env]["database"]
    collate = 'utf8mb4_unicode_ci'
    char_set = 'utf8mb4'
    row_format = 'DYNAMIC'

    execute("ALTER DATABASE #{db_name} CHARACTER SET #{char_set} COLLATE #{collate};")
 
    ActiveRecord::Base.connection.tables.each do |table|
      execute("ALTER TABLE #{table} ROW_FORMAT=#{row_format};")
      execute("ALTER TABLE #{table} CONVERT TO CHARACTER SET #{char_set} COLLATE #{collate};")
    end
  end
end

(Based on this post.)