Merge pull request rails#51330 from HugoWenTD/main

Add some description for MariaDB in ActiveRecord documentation

Author: skipkayhil

guides/source/active_record_basics.md

@@ -130,9 +130,9 @@ Active Record uses conventions for column names in the database tables as well,
 depending on the purpose of these columns.
 
 * **Primary keys** - By default, Active Record will use an integer column named
-  `id` as the table's primary key (`bigint` for PostgreSQL and MySQL, `integer`
-  for SQLite). When using [Active Record Migrations](#migrations) to create your
-  tables, this column will be automatically created.
+  `id` as the table's primary key (`bigint` for PostgreSQL, MySQL, and MariaDB,
+  `integer` for SQLite). When using [Active Record Migrations](#migrations) to
+  create your tables, this column will be automatically created.
 * **Foreign keys** - These fields should be named following the pattern
   `singularized_table_name_id` (e.g., `order_id`, `line_item_id`). These are the
   fields that Active Record will look for when you create associations between
@@ -657,8 +657,8 @@ class CreatePublications < ActiveRecord::Migration[7.2]
 end
 ```
 
-Note that the above code is database-agnostic: it will run in MySQL, PostgreSQL,
-SQLite, and others.
+Note that the above code is database-agnostic: it will run in MySQL, MariaDB,
+PostgreSQL, SQLite, and others.
 
 Rails keeps track of which migrations have been committed to the database and
 stores them in a neighboring table in that same database called

guides/source/active_record_querying.md

@@ -2714,7 +2714,7 @@ and may yield this for PostgreSQL:
 
 ### Explain Options
 
-For databases and adapters which support them (currently PostgreSQL and MySQL), options can be passed to provide deeper analysis.
+For databases and adapters which support them (currently PostgreSQL, MySQL, and MariaDB), options can be passed to provide deeper analysis.
 
 Using PostgreSQL, the following:
 

guides/source/active_record_validations.md

@@ -762,9 +762,9 @@ In order to add a uniqueness database constraint on your database, use the
 
 Should you wish to create a database constraint to prevent possible violations
 of a uniqueness validation using the `:scope` option, you must create a unique
-index on both columns in your database. See [the MySQL manual][] for more
-details about multiple column indexes or [the PostgreSQL manual][] for examples
-of unique constraints that refer to a group of columns.
+index on both columns in your database. See [the MySQL manual][] and [the MariaDB
+manual][] for more details about multiple column indexes, or [the PostgreSQL
+manual][] for examples of unique constraints that refer to a group of columns.
 
 There is also a `:case_sensitive` option that you can use to define whether the
 uniqueness constraint will be case sensitive, case insensitive, or if it should
@@ -791,6 +791,7 @@ See [`validates_uniqueness_of`][] for more information.
 [`validates_uniqueness_of`]: https://api.rubyonrails.org/classes/ActiveRecord/Validations/ClassMethods.html#method-i-validates_uniqueness_of
 [`add_index`]: https://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/SchemaStatements.html#method-i-add_index
 [the MySQL manual]: https://dev.mysql.com/doc/refman/en/multiple-column-indexes.html
+[the MariaDB manual]: https://mariadb.com/kb/en/compound-composite-indexes/
 [the PostgreSQL manual]: https://www.postgresql.org/docs/current/static/ddl-constraints.html
 
 ### `validates_associated`