MySQL's MIN and MAX functions are for aggregations only. This will not work and produce an error: SELECT id, MIN(birthday, '1978-01-01') FROM users;
...note that while this note has a number of code examples in Ruby and MySQL, the concepts apply to all programming languages and data stores. When to round
...of rounded values. Don't ever use the float data type in Ruby or MySQL The data types Float (Ruby) and FLOAT (MySQL) are not suited for calculating or storing...
If you need to do calculations inside the database and can not use Ruby objects you may run into problems...
...wide mutex on something that is not a row, check out: Simple database mutex (MySQL lock). PostgreSQL: How to use with_advisory_lock to prevent race conditions
Use this MySQL command to show further info about a table: SHOW CREATE TABLE tags; This will output a table schema like this: CREATE TABLE `tags` ( `id` int(11) NOT...
...json and array take away a lot of the pain that you had on MySQL projects. Example use cases for array are tags or storing foreign keys (instead of a...
MMM (MySQL Master-Master Replication Manager) is a set of flexible scripts to perform monitoring/failover and management of MySQL Master-Master replication configurations (with only one node writable at any...
Occasionally some complex query must be processed on the database because building thousands of Ruby objects is impracticable.
If you need to export data from MySQL to a CSV, you can profit from really fast built-in methods. This query writes the data to /tmp/geodb_coodinates.csv. And it's...
This might be due to AppArmor denying the MySQL server access to most of the filesystem. You can instead use LOAD DATA LOCAL INFILE ... to pipe data through the MySQL...
To clear the query cache in your MySQL database manually, e.g. for database profiling, execute the following command in your MySQL console: RESET QUERY CACHE...
...some deliberation, we decided to implement a "schema-less" storage system on top of MySQL rather than use a completely new storage system. This post attempts to describe the high...
Store schema-less data in MySQL...
...be useful to have a Ruby expression like condition ? positive_case : negative_case in MySQL queries: UPDATE users SET monthly_debit = IF(subscriber...
...mix dates and times incomparisons, mind to not compare datetimes with date ranges in MySQL. Visualisation 1. ------- ------- AAA AAA BBB BBB ------- ------- 2. ------- AAA B ------- 3. ------- A BBB ------- 4. ------- AAA
Installiere die folgenden Komponenten mit Ansible in diesem Container: Nginx PHP-FPM Datenbank (MySQL / MariaDB) Eine Wordpress Installation Wordpress (bzw. der PHP Prozess, welcher den Code ausführt) soll mit...
...Nginx, mehrere PHP-FPM Konfigurationen, mehrere User). Dafür müssen auch mehrere Datenbanken in der MySQL Installation angelegt werden können. Achte auf ein gutes Setup mit Roles und dem Playbook. Bedenke...
Take care in queries where multiple AND or OR operators are used. In doubt, always use braces to enforce precedence...
Some advice for bulk loading many records into InnoDB and finishing before the sun burns out. Use with care.
...will resemble your database's EXPLAIN style. For example, it looks like this on MySQL: User.where(id: 1).includes(:articles).explain EXPLAIN for: SELECT `users`.* FROM `users` WHERE `users`.`id...
...will make a single query. It uses a sub-query, which is slow in MySQL, but fast in PostgreSQL: SELECT * FROM posts WHERE user_id IN (SELECT id FROM users...
...invoice.products # => [# ] How the :uniq option works In the example above it changes the MySQL query for Invoice#products to something like SELECT DISTINCT * FROM products ... Issues with PostgreSQL
Enabling this shows each column in a own line. It's similar to mysql \G \x on Prevent users FROM connecting to a database ALTER DATABASE foo_db CONNECTION...
They don't teach you this in college, but the fundamental theorem of the software industry is the idea that...
...engineering of your source code you might consider adding a comment. Both PostgreSQL and MySQL support comments in the DB schema: For new columns: https://guides.rubyonrails.org/active_record_migrations.html#comments Changing the comment...