column_for will raise in case column is not found for the given table,
so there is no need to handle that here.

For mysql2/mysql adapters, `sql_mode` variable name set in `database.yml`
as string, was ignored and `sql_mode` was set to use strict mode.

Fixes #14895

this lets arel know how to correctly quote the value

* cache `o.name` value
* Avoid extra `concat` call
* Avoid extra `<<` call

Also:
  - updates tests by stubbing table_exists? method
  - adds entry for creating indexes in CREATE TABLE to changelog

This is important, because adding an index on a temporary table after
it has been created would commit the transaction

Conflicts:
	activerecord/CHANGELOG.md

Blast from the past, MySQL 4 era, when the password hashing style changed.

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

Only use BINARY for mysql case sensitive uniqueness check when column has a case insensitive collation.

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.