You can create foreign keys in the following way (we are running queries with Arctype for this example): Creating Tables with Foreign Keys Generally, big data refers to a lot of rows – for a data set to be considered in the “big data” range, it should have at least a hundred million rows, and the values should be preferably distinct as well.įoreign keys, on the other hand, are columns that are used to link data between tables – in other words, foreign keys are used to link data existing in one table to another. Well, generally, everything in this space is very simple – big data refers to any data set that is so large that it is sometimes deemed unusable by a system. What is Big Data and What are Foreign Keys?īefore diving further into big data sets and its interaction with foreign keys, we would need to explain what big data is. In this blog, we will dive deeper into the correlation between big data and foreign keys on MySQL. If you’re reading this post, also chances are that you know a couple of things about storage engines, indexes, partitioning, normalization, search engines helping you secure your data, and whatnot. Though one can also set user fields to null instead of deleting the row completely, and in that case you would go with solution number one as one would never actually need to fully delete a user record.If you find yourself reading this post, there are very good chances that you find yourself in the shoes of a MySQL database administrator, a database-savvy developer, or even a sysadmin. If the clinic does not care about history of the appointments then you can go with solution number one. In this way when user is deleted you will still have the appointment in the db, but the user_id will be null as that user does not exist anymore. In this case you would go with solution number 2. But the clinic still wants to keep history of all the appointments in the db. Lets say this is for a clinic and the clinic gets a request from a user to delete him from the db. Add on delete set null meaning that when user is deleted appointments user_id relating to that user should be set to null (though you will have to change user_id int(10) UNSIGNED NOT NULL to user_id int(10) UNSIGNED DEFAULT NULL.Add on delete cascade meaning that when user is deleted appointments relating to that user should also be deleted as suggested by Shadow (point number two).There are a couple of options, but in the end there are really only two main options: `updated_at` timestamp NULL DEFAULT NULL,ĪDD KEY `appointments_doctor_id_foreign` (`doctor_id`),ĪDD KEY `appointments_user_id_foreign` (`user_id`) ĪDD CONSTRAINT `appointments_doctor_id_foreign` FOREIGN KEY (`doctor_id`) REFERENCES `doctors` (`id`),ĪDD CONSTRAINT `appointments_user_id_foreign` FOREIGN KEY (`user_id`) REFERENCES `users` (`id`) `date` varchar(191) COLLATE utf8mb4_unicode_ci NOT NULL, `time` varchar(191) COLLATE utf8mb4_unicode_ci NOT NULL, ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci Īppointments table CREATE TABLE `appointments` ( `created_at` timestamp NULL DEFAULT NULL, `remember_token` varchar(100) COLLATE utf8mb4_unicode_ci DEFAULT NULL, `dateofbirth` varchar(191) COLLATE utf8mb4_unicode_ci NOT NULL, `password` varchar(191) COLLATE utf8mb4_unicode_ci NOT NULL, `email` varchar(191) COLLATE utf8mb4_unicode_ci NOT NULL, `postcode` varchar(191) COLLATE utf8mb4_unicode_ci NOT NULL, `address` varchar(191) COLLATE utf8mb4_unicode_ci NOT NULL, `surname` varchar(191) COLLATE utf8mb4_unicode_ci NOT NULL, `firstname` varchar(191) COLLATE utf8mb4_unicode_ci NOT NULL, Not sure if it changes anything but just incase I created the tables using laravel I'm getting this error when trying to delete a user from the database, I know it's doing this because the user I'm trying to delete is a foreign key in the appointments table, but I don't know how to correct it or where I have gone wrong.
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