In some cases the Comparator class returns multiple drops for the same foreign key.
Specifically, in case you have two tables, A & B, with A having a foreign key FK
referencing B, if you drop table B, the resulting diff shows this FK twice,
once on the diff->orphanedForeignKeys array as we're deleting B, and another on
the diff->changedTables array as table A is also being modified. As a result of this you
get the DROP FOREIGN KEY instruction twice in the final SQL.

[DDC-1657] Prevent autoincrement sequences from creating DROP SEQUENCE statements because of old/new schema missmatch.

[DBAL-204] Sane refactoring of the previous idea. Removed a bunch of code again and implemented proper schema namespacing. Also got the wording right (hopefully) and fixed the algorithms.

DBAL-112, DBAL-113 - Implement AbstractPlatform::getAlterSequenceSQL() and fix comparator code for sequences

[DBAL-42] Optimized column comment change detection. Ignore from columns with a null comment which indicates not set compared to an empty string which says delete comment.

[DBAL-42] Add support to reverse engineer Comments from MySQL, PostgreSQL and ORacle into Doctrine\DBAL\Schema\Column instances and added comment comparison into Comparator.

DBAL-50 - Explicitly add an index for each foreign key added to a Schema\Table instance. Removed code to FixSchema based on foreign keys, since assumptions now dont apply anymore. Refactored algorithms to check for duplicate or potential overrule indexes into Schema\Index classes, added tests and unified Table API handling these conflicts

Temporary fix for issues appearing due to DBAL-2 reopening, found an actual additional bug that is now fixed in PostgresSQL Schema Manager

Fix change to Postgresql NULL Column detection

Temporary fix for issues appearing due to DBAL-2 reopening, found an actual additional bug that is now fixed in PostgresSQL Schema Manager

[2.0] DDC-396 - Fixed bug with RESTRICT/NO ACTION and PHP NULL not valued as the same in Schema Foreign Key Diff

[2.0] DDC-214, DDC-303, DDC-304 - Fix several errors with Schema Inference from Database and Metadata and Comparisons, aswell as related bugs in DatabaseDriver. DDC-305 - Abstracted TRUNCATE command for all platforms.

[2.0] DDC-169 - Finished ALTER Table TableDiff refactoring, adding code to handle index and FK changes. Added a general functional test for alter table against all platforms.

[2.0] DDC-169 - AbstractPlatform::getAlterTableSql() now accepts only a TableDiff instance as argument across all platforms.