Currently blank comment does not dump to `db/schema.rb`. But created it
even if specified blank.

invalid column type
    /activerecord/lib/active_record/connection_adapters
    /abstract/schema_definitions.rb:306
    type = type.to_sym

Changed to the following to handle nil case:
    type = type.to_sym if type

Added regression test for this case:
  /activerecord/test/cases/migration_test.rb:554
  if current_adapter?(:SQLite3Adapter)
    def test_allows_sqlite3_rollback_on_invalid_column_type
      Person.connection.create_table :something, force: true do |t|
        t.column :number, :integer
        t.column :name, :string
        t.column :foo, :bar
      end
      assert Person.connection.column_exists?(:something, :foo)
      assert_nothing_raised { Person.connection.remove_column :something, :foo, :bar }
      assert !Person.connection.column_exists?(:something, :foo)
      assert Person.connection.column_exists?(:something, :name)
      assert Person.connection.column_exists?(:something, :number)
    ensure
      Person.connection.drop_table :something, if_exists: true
    end
  end

Style/SpaceBeforeBlockBraces
Style/SpaceInsideBlockBraces
Style/SpaceInsideHashLiteralBraces

Fix all violations in the repository.

If you call `remove_index` with wrong options, say a type, like I did,
you get:

```
== 20160810072541 RemoveUniqueIndexOnGoals: migrating =========================
-- remove_index(:goal, {:coulmn=>:kid_id, :unique=>true})
rails aborted!
StandardError: An error has occurred, this and all later migrations canceled:

undefined method `ArgumentError' for #<ActiveRecord::ConnectionAdapters::PostgreSQLAdapter:0x007fb7dec91b28>
```

What happened is that I mistyped column (coulmn) and got a
`NoMethodError`, because of a missing comma during the raise. This made
Ruby think we're calling the method `ArgumentError`.

The current code base is not uniform. After some discussion,
we have chosen to go with double quotes by default.

- Followup of https://github.com/rails/rails/pull/23179.

Keeps schema migration inserts as a single commit, so we still get all of the
benefits of https://github.com/rails/rails/commit/42dd2336b31a8d98776d039a2b9fd7f834156a78,
but allows for easier git diff-ing. Fixes #25504.

This includes minor grammar fixes throughout the file.

Actually schema dumper/creation supports composite primary key (#21614).
Therefore it should not show the warning about composite primary key in
connection adapter.

This change moves the warning to `AttributeMethods::PrimaryKey` and
suppress the warning for habtm join table.

Fixes #25388.

- Followup of https://github.com/rails/rails/commit/1ea6cc11211dc89e3e14b2b641a3cca8a0a91d55.

The code incorrectly assumes that the option was written as
`foreign_key: true`, but that is not always the case. This now mirrors
the behavior of reverting `add_foreign_key`. The code was changed to use
kwargs while I was touching it, as well.

This could really use a refactoring to go through the same code paths as
`add_refernce` in the future, so we don't duplicate default values.

Fixes #25169

Example:

    create_table :users do |t|
      t.string :name
      t.index 'lower(name) varchar_pattern_ops'
    end

Fixes #19090.
Fixes #21765.
Fixes #21819.
Fixes #24359.
Signed-off-by: NJeremy Daer <jeremydaer@gmail.com>

There is no need to fetch all table indexes in remove_index if name is specified. If name is wrong, then StatementInvalid will be raised.
Signed-off-by: NJeremy Daer <jeremydaer@gmail.com>

Follow up to #24685. `insert_versions_sql` is not public API.

Re. 6e098284

https://github.com/rails/rails/commit/42dd2336b31a8d98776d039a2b9fd7f834156a78 changed INSERT INTO versions to run in 1 single query.
This breaks for sqlite versions < 3.7.11, which is especially the case on Ubuntu 12.04 LTS, that has SQLite version 3.7.9 as default.

So we check for support for multi insert, before performing single query inserts, else fallback to older version of running multiple queries.
[Vipul A M & Yasuo Honda]

Follow up to #24221.

* Switch to keyword args where we can without breaking compat.
* Use add_table_options! for :options, too.
* Some code polish.

- Add link for finding the addional options for index.
- Add example for unique index as this is a common requirement.
- Add link in guide for index options.

Comments are specified in migrations, stored in database itself (in its schema),
and dumped into db/schema.rb file.

This allows to generate good documentation and explain columns and tables' purpose
to everyone from new developers to database administrators.

For PostgreSQL and MySQL only. SQLite does not support comments at the moment.

See docs for PostgreSQL: http://www.postgresql.org/docs/current/static/sql-comment.html
See docs for MySQL: http://dev.mysql.com/doc/refman/5.7/en/create-table.html

Fix description for method ActiveRecord::ConnectionAdapters::SchemaStatements#add_timestamps [ci skip]

The comments of add_foreign_key method was displaying incorrect constraint name.

Follow up to #23508.

https://dev.mysql.com/doc/refman/5.7/en/innodb-fulltext-index.html
https://dev.mysql.com/doc/refman/5.7/en/creating-spatial-indexes.html

`initialize_schema_migrations_table` is called in every migrations.

https://github.com/rails/rails/blob/v5.0.0.beta1/activerecord/lib/active_record/migration.rb#L1080
https://github.com/rails/rails/blob/v5.0.0.beta1/activerecord/lib/active_record/schema.rb#L51

This means that extra `show variables` is called regardless of the
existence of `schema_migrations` table.

This change is to avoid extra `show variables` if `schema_migrations`
table exists.

`ActiveRecord::ConnectionAdapters::SchemaStatements#columns` is defined
here as an interface method here. So changes to raise `NotImplementedError`
same as `tables`, `views` ...etc.

If `AR.primary_key` is called for a table who has composite primary key,
the method returns `nil`. This behavior sometimes generates invalid SQL.
The first time developers notice to invalid SQL is when they execute
SQL. This commit enables developers to know they are doing something
dangerous as soon as possible.

This line causes an error when executing the command: `rails db:drop db:create db:schema:load`

ActiveRecord::StatementInvalid: PG::SyntaxError: ERROR:  syntax error at or near "{"
LINE 1: ...NSERT INTO "schema_migrations" (version) VALUES (#{v}), (#{v...

We found that inserting all 600 schema_migrations for our mid-sized app takes about a minute on a cloud based CI environment.

I assume that the original code did not use multi-row-insert because SQLite3 was not supporting the syntax back then,
but it's been supported since 3.7.11: http://www.sqlite.org/releaselog/3_7_11.html