I was having some trouble querying dates on a Rails project. Let's see some tips...

WRONG:

User.where("created_at >= '#{date_start}'")
    .where("created_at <= '#{date_end}'")

Produces:

"SELECT \"users\".* FROM \"users\" WHERE (created_at >= '2015-08-11 00:00:00 -0300') AND (created_at <= '2015-08-11 23:59:59 -0300')"

And Postgresql won't parse the date the right way.

RIGHT:

User.where("created_at >= ?", date_start)
    .where("created_at <= ?", date_end)

Produces:

"SELECT \"users\".* FROM \"users\" WHERE (created_at >= '2015-08-11 03:00:00.000000') AND (created_at <= '2015-08-12 02:59:59.999999')"

Ok case...

BETTER:

User.where(created_at: (date_start..date_end))

Produces:

"SELECT \"users\".* FROM \"users\" WHERE (\"users\".\"created_at\" BETWEEN '2015-08-11 03:00:00.000000' AND '2015-08-12 02:59:59.999999')"

This is the preferred method because it "namescopes" the attribute with the table_name.