Support for mysql alter column add auto_increment attribute

[emosbaugh]

Altering a column and adding auto_increment when a table is not empty gives error Error 1062: ALTER TABLE causes auto_increment resequencing, resulting in duplicate entry '1' for key. This relies on prepared statements to add auto_increment with increment value transactionally. A connection with multiStatements=true is required.

[emosbaugh]

I am concerned about enabling multi-statements here

https://github.com/go-sql-driver/mysql#multistatements

Allow multiple statements in one query. While this allows batch queries, it also greatly increases the risk of SQL injections. Only the result of the first query is returned, all other results are silently discarded.

[emosbaugh]

I suggest only supporting this if multistatements are enabled rather than appending this to the connection string.

[divolgin]

How about instead of multi-statements we add transaction to the ddl?

START TRANSACTION;
set @max = (select coalesce(max(`id`), 0) + 1 from `users`);
set @alter_statement = concat('alter table `users` change column `id` `id` int (11) not null auto_increment, auto_increment=', @max);
prepare stmt from @alter_statement; execute stmt; deallocate prepare stmt;
COMMIT;

and in code add a hardcoded statement when transaction is detected to
defer ROLLBACK