Update database guides on text data type usage

- Add Strings and the Text data type style guide
- Add section on text columns on the Migration Style Guide
- Add index.md to doc/development/database/

doc/development/README.md

@@ -113,50 +113,7 @@ Complementary reads:
 
 ## Database guides
 
-### Tooling
-
-- [Understanding EXPLAIN plans](understanding_explain_plans.md)
-- [explain.depesz.com](https://explain.depesz.com/) for visualizing the output
-  of `EXPLAIN`
-- [pgFormatter](http://sqlformat.darold.net/) a PostgreSQL SQL syntax beautifier
-
-### Migrations
-
-- [What requires downtime?](what_requires_downtime.md)
-- [SQL guidelines](sql.md) for working with SQL queries
-- [Migrations style guide](migration_style_guide.md) for creating safe SQL migrations
-- [Testing Rails migrations](testing_guide/testing_migrations_guide.md) guide
-- [Post deployment migrations](post_deployment_migrations.md)
-- [Background migrations](background_migrations.md)
-- [Swapping tables](swapping_tables.md)
-- [Deleting migrations](deleting_migrations.md)
-
-### Debugging
-
-- Tracing the source of an SQL query using query comments with [Marginalia](database_query_comments.md)
-- Tracing the source of an SQL query in Rails console using [Verbose Query Logs](https://guides.rubyonrails.org/debugging_rails_applications.html#verbose-query-logs)
-
-### Best practices
-
-- [Adding database indexes](adding_database_indexes.md)
-- [Foreign keys & associations](foreign_keys.md)
-- [Single table inheritance](single_table_inheritance.md)
-- [Polymorphic associations](polymorphic_associations.md)
-- [Serializing data](serializing_data.md)
-- [Hash indexes](hash_indexes.md)
-- [Storing SHA1 hashes as binary](sha1_as_binary.md)
-- [Iterating tables in batches](iterating_tables_in_batches.md)
-- [Insert into tables in batches](insert_into_tables_in_batches.md)
-- [Ordering table columns](ordering_table_columns.md)
-- [Verifying database capabilities](verifying_database_capabilities.md)
-- [Database Debugging and Troubleshooting](database_debugging.md)
-- [Query Count Limits](query_count_limits.md)
-- [Creating enums](creating_enums.md)
-
-### Case studies
-
-- [Database case study: Filtering by label](filtering_by_label.md)
-- [Database case study: Namespaces storage statistics](namespaces_storage_statistics.md)
+See [database guidelines](database/index.md).
 
 ## Integration guides
 

doc/development/database/index.md

+# Database guides
+
+## Tooling
+
+- [Understanding EXPLAIN plans](../understanding_explain_plans.md)
+- [explain.depesz.com](https://explain.depesz.com/) for visualizing the output
+  of `EXPLAIN`
+- [pgFormatter](http://sqlformat.darold.net/) a PostgreSQL SQL syntax beautifier
+
+## Migrations
+
+- [What requires downtime?](../what_requires_downtime.md)
+- [SQL guidelines](../sql.md) for working with SQL queries
+- [Migrations style guide](../migration_style_guide.md) for creating safe SQL migrations
+- [Testing Rails migrations](../testing_guide/testing_migrations_guide.md) guide
+- [Post deployment migrations](../post_deployment_migrations.md)
+- [Background migrations](../background_migrations.md)
+- [Swapping tables](../swapping_tables.md)
+- [Deleting migrations](../deleting_migrations.md)
+
+## Debugging
+
+- Tracing the source of an SQL query using query comments with [Marginalia](../database_query_comments.md)
+- Tracing the source of an SQL query in Rails console using [Verbose Query Logs](https://guides.rubyonrails.org/debugging_rails_applications.html#verbose-query-logs)
+
+## Best practices
+
+- [Adding database indexes](../adding_database_indexes.md)
+- [Foreign keys & associations](../foreign_keys.md)
+- [Adding a foreign key constraint to an existing column](add_foreign_key_to_existing_column.md)
+- [Strings and the Text data type](strings_and_the_text_data_type.md)
+- [Single table inheritance](../single_table_inheritance.md)
+- [Polymorphic associations](../polymorphic_associations.md)
+- [Serializing data](../serializing_data.md)
+- [Hash indexes](../hash_indexes.md)
+- [Storing SHA1 hashes as binary](../sha1_as_binary.md)
+- [Iterating tables in batches](../iterating_tables_in_batches.md)
+- [Insert into tables in batches](../insert_into_tables_in_batches.md)
+- [Ordering table columns](../ordering_table_columns.md)
+- [Verifying database capabilities](../verifying_database_capabilities.md)
+- [Database Debugging and Troubleshooting](../database_debugging.md)
+- [Query Count Limits](../query_count_limits.md)
+- [Creating enums](../creating_enums.md)
+
+## Case studies
+
+- [Database case study: Filtering by label](../filtering_by_label.md)
+- [Database case study: Namespaces storage statistics](../namespaces_storage_statistics.md)

doc/development/migration_style_guide.md

@@ -727,6 +727,12 @@ Rails migration example:
 add_column(:projects, :foo, :integer, default: 10, limit: 8)
 ```
 
+## Strings and the Text data type
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/30453) in GitLab 13.0.
+
+See the [text data type](database/strings_and_the_text_data_type.md) style guide for more information.
+
 ## Timestamp column type
 
 By default, Rails uses the `timestamp` data type that stores timestamp data