Currently Database Schema checker (Database FIX) button is ignoring

• NULL column attribute
• DEFAULT column attribute

e.g. this is not checked

ALTER TABLE `table1` MODIFY `colname1` NOT NULL DEFAULT 'somevalue'

Also this is applied only when column is of wrong name

ALTER TABLE `table1` CHANGE `colname_old` `colname_new` NOT NULL DEFAULT 'somevalue'

Thus the above query will not run if column is correct name despite NULL and DEFAULT attributes being of wrong value

Summary of Changes

Modify Schema checker to support checking the above
(modified and tested Mysql / Maria DB, someone should help with the other DBs)

Testing Instructions

View an 'upgrade' SQL file that has

ALTER TABLE 'table1' MODIFY/CHANGE ...

e.g.
administrator/components/com_admin/sql/updates/mysql/3.7.0-2016-11-04

ALTER TABLE `#__extensions` CHANGE `enabled` `enabled` TINYINT(3) NOT NULL DEFAULT '0';

-- Go to a DB manager e.g. phpmyadmin and change it to NULL
Run the DB Fixer and you will be ask to fix it (back to NOT NULL)

-- Go to a DB manager e.g. phpmyadmin and change DEFAULT to '1'
Run the DB Fixer and you will be ask to fix it (back to '0')

If your apply this PR to some older installations e.g. a J2.5 upgraded up to staging,
then probably you will find several errors ... already being there

Expected result

Database Schema checker (Database FIX) supports checking
queries like: ALTER TABLE 'table1' MODIFY/CHANGE

• NULL column attribute
• DEFAULT column attribute

Actual result

The above are not checked

Documentation Changes Required

None