Convert UTC timestamp into EST date and time using SQL

Question

I have downloaded a bunch of tweets from the Twitter API. As I understand, the (JSON) created_at property is given in UTC (indicated by the +0000):

created_at: Fri Feb 18 21:08:38 +0000 2011

In my script, I stored these dates as a unix timestamp by converting them using PHP's strtotime:

strtotime(Fri Feb 18 21:08:38 +0000 2011) = 1298063318

I thus now have a table with tweets, with UTC unix timestamps:

id  nyse_date   nyse_time  twitter_timestamp
-------------------------------------------
1   2011-02-18  16:08:38   1298063318

The tweets I gathered all talk about stocks of the NYSE. The NYSE, (in New York, obviously), is located in EST, which is UTC - 5 hours (or: 18.000 seconds). So a tweet written on UTC Fri Feb 18 21:08:38 2011 is written on NYSE time on Fri Feb 18 16:08:38 2011. Hence, (see the table) a 1298063318 UTC timestamp is stored converted to EST (NYSE) date and time.

I now need to do this for all (millions of) tweets in the table. With what query can I automate this? I get heavily confused when I think about UTC timestamps of for instance

Fri Feb 18 02:08:38 +0000 2011

Here, nyse_date would be 2011-02-17 (not: 18) and nyse_time 21:08:38.

I'm hoping for some SQL goodness, because this is heavily confusing me (probably needlessly but it's my first time working with timestamps and timezones)

Answer 1

After reading in your data, update the twitter_timestamp field, like in

update mydata set twitter_timestamp = twitter_timestamp - 5 * 3600;