Question

@events = Event.all(:order => "date DESC")

to order my events by date, a datetime column.

Is it possible to order them not by date, but only by hour? (I’m suing sqlite3 database)

Thanks!

Answer 1

For SQLite,

@events = Event.all(:order => "time(date) DESC")

Use that with care, because it ignores the date. (And see “Moments later” below.)

CREATE TABLE test (date datetime primary key);
INSERT INTO "test" VALUES('2011-01-01 08:00:00');
INSERT INTO "test" VALUES('2011-01-01 08:13:00');
INSERT INTO "test" VALUES('2011-01-01 09:23:00');
INSERT INTO "test" VALUES('2011-01-02 09:15:00');

Only one of the dates is on Jan 2.

sqlite> select * from test order by time(date) desc;
2011-01-01 09:23:00
2011-01-02 09:15:00
2011-01-01 08:13:00
2011-01-01 08:00:00

Moments later . . .

I realized you wanted to sort by hour, not by time. That questionable requirement takes a different expression, and sorts differently.

@events = Event.all(:order => "strftime('%H', date) DESC")

sqlite> select date from test order by strftime('%H', date) desc;
2011-01-01 09:23:00
2011-01-02 09:15:00
2011-01-01 08:00:00
2011-01-01 08:13:00

The last two rows are sorted correctly by hour, incorrectly by time.

Still later . . .

The OP deploys on Heroku, which doesn’t support SQLite. To sort by hour descending, the OP probably needs something like

@events = Event.all(:order => "extract (hour from date) DESC")

And stop using one platform for development and a different platform for deployment.