Oracle database itself does not have `bigint` SQL type, then it gets `ORA-00902: invalid datatype`.

It can be addressed by using ActiveRecord `bigint` type
because Oracle enhanced adapter recognizes ActiveRecord `bigint` type
and transfer it to its equivalent SQL type `NUMBER(19)`.

primary_keys(table) needs to query various metadata tables in Postgres
to determine the primary key for the table. Previously, it did so using
a complex common table expression against pg_constraint and
pg_attribute.

This patch simplifies the query by using information_schema tables.
This simplifies the logic, making the query far easier to understand,
and additionally avoids an expensive unnest, window function query, and
common table expression.

The `default` arg of `index_name_exists?` is only used the adapter does
not implemented `indexes`. But currently all adapters implemented
`indexes` (See #26688). Therefore the `default` arg is never used.

Closes #27980

Closes #27979

`supports_primary_key?` was added to determine if `primary_key` is
implemented in the adapter in f0602214. But we already use `primary_key`
without `supports_primary_key?` (207f266c, 5f3cf424) and using
`supports_primary_key?` has been removed in #1318. This means that
`supports_primary_key?` is no longer used in the internal and Active
Record doesn't work without `primary_key` is implemented (all adapters
must implement `primary_key`).

Closes #27977

These files are not using `strip_heredoc`.

Closes #27976

So queries are not run against the previous table name.

Closes #27953

This was never really intended to work (at least not without calling
`define_attribute_methods`, which is less common with Active Record). As
we move forward the intention is to require the use of `attribute` over
`attr_accessor` for more complex model behavior both on Active Record
and Active Model, so this behavior is deprecated.

Fixes #27956.
Close #27963.

[Alex Serban & Sean Griffin]

Currently schema dumper lost the unsigned option when primary key is
defined as bigint with unsigned. This commit fixes the issue.

Closes #27960

`test_composite_primary_key_out_of_order` should use `barcodes_reverse`
table.

primary_keys(table) needs to query various metadata tables in Postgres to
determine the primary key for the table. Previously, it did so using a
complex common table expression against pg_constraint and pg_attribute.

This patch simplifies the query by joining pg_index against pg_attribute
instead of going through pg_constraint. This avoids an expensive unnest,
window function query, and common table expression.

EXPLAINing these queries in Postgres against a database with a single
table with a composite primary key shows a 66% reduction in the plan and
execute latencies. This is significant during application startup time,
especially against very large schemas, where these queries would be even
slower and more numerous.

Closes #27949

Column options are passed as an hash args then used as `options` hash in
`add_column_options!`. Converting args to attributes is inconvinient for
using options as an hash.

This reverts commit 28977f1f.

If select clause is specified and last column has a column alias,
additional column alias causes a statement invalid.

Add test coverage for counting a single column with NULL values.

Fixes #27676, #27682, and #27705.

Follow up to #26266.

The default type of `primary_key` and `references` were changed to
`bigint` since #26266. But legacy migration and sqlite3 adapter should
keep its previous behavior.

`ColumnDumper#migration_keys` was extracted to customize keys for
standardized column arguments widths. But the feature was removed in
df84e986. The internal method is no longer used for that.

Since text default treated as an empty string in non-strict mode has
been removed in #26154, `MySQL::Column` behaves like any other column.
Also, The difference between strict and non-strict mode is covered by
`test_mysql_not_null_defaults_strict` and `test_mysql_not_null_defaults_non_strict`.

```
go get -u github.com/client9/misspell/cmd/misspell
misspell  -w -error -source=text .
```

Some custom primary key tests (added at #17631, #17696, #18220, #18228)
were lost at #26266. Restore the tests to improve test coverage.

The PR #27384 changed migration compatibility behaviour.

```ruby
class CreateMasterData < ActiveRecord::Migration[5.0]
  def change
    create_table :master_data, id: :integer do |t|
      t.string :name
    end
  end
end

```

Previously this migration created non-autoincremental primary key
expected. But after the PR, the primary key changed to autoincremental,
it is unexpected.

This change restores the behaviour of the compatibility layer.

And raise `ArgumentError` when passing string to define callback.

The PR #27384 changed integer-like primary key to be autoincrement
unless an explicit default. This means that integer-like primary key is
restored as autoincrement unless dumping the default nil explicitly.
We should dump integer-like primary key with default nil correctly.

When the association's primary key is manually set as a symbol and called with an array of strings, CollectionAssociation#ids_writer
fails to cast the ids to integers. This is because
AssociationReflection#association_primary_key_type and
ThroughReflection#association_primary_key_type return the incorrect
type, since ModelSchema.type_for_attribute only accepts a string. The
result is an ActiveRecord::RecordNotFound error.

MySQL generated columns: https://dev.mysql.com/doc/refman/5.7/en/create-table-generated-columns.html
MariaDB virtual columns: https://mariadb.com/kb/en/mariadb/virtual-computed-columns/

Declare virtual columns with `t.virtual name, type: …, as: "expression"`.
Pass `stored: true` to persist the generated value (false by default).

Example:

    create_table :generated_columns do |t|
      t.string  :name
      t.virtual :upper_name, type: :string,  as: "UPPER(name)"
      t.virtual :name_length, type: :integer, as: "LENGTH(name)", stored: true
      t.index :name_length  # May be indexed, too!
    end

Closes #22589

Fixes #27666.

Fixes #27826
Refer https://github.com/rails/rails/commit/f7b317175430a2d9300d9c4acfc1f34f4fdb2fbc