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Is there an easy way to see the actual SQL generated by a rails migration?
I have a situation where a migration to change a column type worked on my local development machine by partially failed on the production server.
My postgreSQL versions are different between local and production (7 on production, 8 on local) so I'm hoping by looking at the SQL generated on the successful migration locally I can work out a SQL statement to run on production to fix things....
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To check for status, run rails db:migrate:status . Then you'll have a good view of the migrations you want to remove. Then, run rails db:rollback to revert the changes one by one.
When you run db:migrate, rails will check a special table in the database which contains the timestamp of the last migration applied to the database. It will then apply all of the migrations with timestamps after that date and update the database table with the timestamp of the last migration.
If you have already run the migration then you cannot just edit the migration and run the migration again: Rails thinks it has already run the migration and so will do nothing when you run rake db:migrate.
It adds a multi-column index on columns one and two in resources table. The advantage of multi-column index is that it helps when you have a query with conditions on those multiple columns.
Look at the log files: log/development.log locally vs log/production.log on your server.
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