[gentoo-user] [OT] Looking for a tool to produce 'reverse' SQL

[Benjamin Blazke]

Hi,

I'm looking for a tool that given an existing (base)
database schema and an 'update patch' DDL .sql script
on input would produce a 'reverse' script that could
be used to undo the changes done by the patch. For
example:

base.sql:
CREATE TABLE xxx (...);

patch.sql:
CREATE TABLE yyy (...);
ALTER TABLE xxx ADD COLUMN aaa ...;
ALTER TABLE xxx CHANGE column bbb ...

reverse.sql:
DROP TABLE yyy;
ALTER TABLE xxx DROP column aaa;
ALTER TABLE xxx CHANGE column bbb <get this from the
original base schema>

The purpose of this exercise is to have a production
database (MySQL) server that needs to update its
schema once in a while to reflect the changes in the
related application without the need to recreate the
schema from scratch (and possibly losing data). The
reverse.sql script could be later used to rollback the
schema changes at any time, even rollback multiple
patches.

How do people generally solve this? I'm sure this must
be a fairly common problem.

Thanks.

Ben



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