How to convert MySQL datetime field into timestamp using Ruby?

I have two fields:

last_modified : datetime
updated_at    : timestamp

updated_at is a new field which has just been added to the table, last_modified contains accurate dates.

I want to be able to loop through all of the rows in the table, selecting the last_modifed datetime, converting it into a timestamp and saving it in 开发者_运维技巧the new updated_at field.

Have no idea how to do this, any help is much appreciated!

---

Try

update table_name set updated_at=unix_timestamp(last_modified);

I don't why you want to store same data twice. Storing same data twice may result into inconsistency.

If you want timestamp in your code, you can do that in code itself.

---

If your table is called some_table, then you can put this in your migration's up class method:

execute 'UPDATE some_table SET updated_at = last_modifed'

MySQL should be able to convert from datetime to timestamp automatically. In an SQL SET clause, the columns are specific to a single row and the SET applies to all matched rows; without a WHERE clause the UPDATE applies to all rows in the table. Remember that SQL is set-based so everything operates on sets of rows and loops don't really fit the model.

I'm assuming that you're using ActiveRecord as you have a timestamp called updated_at. If you're not using ActiveRecord then you'll have to find another way to send the SQL UPDATE to the database.