since handle_if_exists_options only removes alter_info->flags if the exists {column, fk,partition etc} exists, lets short cut that too.

https://github.com/MariaDB/server/pull/23

for 10.0: https://github.com/MariaDB/server/pull/58

danblack, I don't understand your comment about handle_if_exists_options (and the if() you've added above it). Could you please elaborate on that?

This if statement is considering whether to allow online operations based on the flags. When Alter_info::ALTER_RENAME or Alter_info::ALTER_KEYS_ONOFF is specified we can still do it online so lets mask those out.
alter_info->flags & ~(Alter_info::ALTER_RENAME |Alter_info::ALTER_KEYS_ONOFF would normally be true if we've got some flags incompatible with with online operations.

   if (!(alter_info->flags & ~(Alter_info::ALTER_RENAME |

                               Alter_info::ALTER_KEYS_ONOFF))

alter_info->flags != 0 is added because if no flags (i.e. a plain alter online table xxxx) is specified this above condition is also false resulting in no online being possible.

The only outcome of handle_if_exists is that alter_info->flags&=

under various branches. If alter_info->flags is already 0 we don't need to call this function.

the if condition before handle_if_exists_options is an optional part of the patch. Omit if you feel uncomfortable about it.