By issuing rake -T you have the following database tasks: rake db:create # Create the database from DATABASE_URL or config/database.yml for the current Rails.env (use db:create:all to create all dbs in the config) rake db:drop # Drops the database using DATABASE_URL or the current Rails.env (use db:drop:all to drop all databases) rake db:fixtures:load # Load … Read more
You ask if you can have more than one primary key field and you most certainly can. You can have only one primary key, but that can consist of as many columns as you need to uniquely identify your rows. Use something like this when you are creating your table: CONSTRAINT pk_PersonID PRIMARY KEY (P_Id,LastName) … Read more
You can use F() objects for this. Here is how you import F: from django.db.models import F New in Django 1.1. Calls to update can also use F() objects to update one field based on the value of another field in the model. This is especially useful for incrementing counters based upon their current value. … Read more
Put your delete statement in an Execute SQL Task. Then make it the first component of your flow. The component looks something like this:
There’s now a method disable_ddl_transaction! that allows this, e.g.: class AddIndexesToTablesBasedOnUsage < ActiveRecord::Migration disable_ddl_transaction! def up execute %{ CREATE INDEX CONCURRENTLY index_reservations_subscription_id ON reservations (subscription_id); } end def down execute %{DROP INDEX index_reservations_subscription_id} end end
I once worked with a very large (Terabyte+) MySQL database. The largest table we had was literally over a billion rows. It worked. MySQL processed the data correctly most of the time. It was extremely unwieldy though. Just backing up and storing the data was a challenge. It would take days to restore the table … Read more
To answer your question, yes, it will only run a single match and then break. However, if you’d like to have logic to allow for conditional matching in the update, the CASE statement is rather useful for this. Something like this as an example: MERGE INTO YourTable USING (VALUES (1, 1, NULL), (0, 0, NULL), … Read more
The reason why I usually suggest PostgreSQL before MySQL is because MySQL is far from the standards (SQL-wise). It does not support the use of window functions (8.4 version), common table expressions (8.4), CHECK constraints, EXCEPT/MINUS operator, even FULL OUTER JOINs… Even though you may have never heard of these words, you’ll have to use … Read more
You need to use full path, something like: DB_DATABASE=/home/laravel-project/database/database.sqlite
There are many possible causes for serialization failures. Technically, a deadlock between two transactions is one form of serialization failure, and can potentially happen at any isolation level if there are concurrent modifications to the schema (database structure). Since you’re asking about PostgreSQL, you should be aware that in PostgreSQL this type of serialization failure … Read more