also override drop_table in AbstractMySQLAdapter to properly drop
temporary tables without committing the transaction

Since MySQL 5.7.3 m13 does now allow primary key column is null.

This method is not using the block variable directly since it is calling
yield

also clarify native rename_index support is >= 5.7, not > 5.7

The MySQL connection adapater swallows all StandardError exceptions,
which includes Mysql::Error and Mysql2::Error. The comment in the
exception clause claims errors thrown here indicate that transactions
aren't supported by the server but that isn't necessarily true. It's
possible the MySQL server has gone away and swallowing a failed commit
may let the application return a successful response when the data has
not been saved. Also, replication libraries like Galera require that the
application handle exceptions thrown at BEGIN/COMMIT.

I'm unable to determine what version of MySQL threw an exception for
transactional statements. I tried as far back as 3.23.49 with InnoDB
disabled but BEGIN & COMMIT statements do not throw an error. If there's
a real case for this logic to continue, we could instead push this
behavior into a configuration setting.

The exception swallowing has been there since the beginning:
db045dbb

When the adapter is with prepared statement disabled and the binds array
is not empty the connection adapter will try to set the binds values and
will fail. Now we are checking if the adapter has the prepared statement
disabled.

Fixes #12023

This reverts commit cb1d07e4, reversing
changes made to 754a373e.

Using the mysql2 adapter, boolean values were sometimes being incorrectly cast
to 't' or 'f'. This changes the cast to match the mysql adapter behavior, ie 1 and 0.

removed two instances of add_column_options! from abstract_mysql_adapter

reworked rename_column_sql to remove add_column_options from schema_statements

changed to use new hash syntax.

enum includes text or blob or ... hooked by wrong regex

Adds support for algorithm option in MySQL indexes
Moves USING and algorithm options upstream

The syntax is still specific to the Adapter, so the actual executed string happens
in the corresponding adapter

Created a layer of abstraction for the valid type checking in schema dumper. Now, connection handles the check for valid types so that each database can handle the changes individually.

As of ccc6910c we use `mysqldump` to create the `structure.sql`.
The old `#structure_dump` code is still in AR but never used.

I removed all relevant parts from the code-base.

This reverts commit 408227d9, reversing
changes made to dca0b57d.

We should only type cast when we need to use.

Related to 4b005fb3

When a table or a column is renamed related indexes kept their name. This will lead to confusing names. This patch renames related indexes when a column or a table is renamed. Only indexes with names generated by rails will be renamed. Indexes with custom names will not be renamed.

It was supposed to be removed by the preceding two reversions but I did
them in the wrong order.

This reverts commit 5d528f83.

Relates to f8c8ad56 which is also getting reverted due to failing test.

* Fix Migration#reversible by not using `transaction`.

* Adapt mysql adapter to updated api for remove_column

* Update test after aedcd683

in the new 'variables:' hash in each database config section in database.yml.
The key-value pairs of this hash will be sent in a 'SET key = value, ...'
query on new database connections.

The configure_connection methods from mysql and mysql2 into are
consolidated into the abstract_mysql base class.