It keeps the current value in localtime and sets the timezone to your localtime&#39;s offset:

    create table a(t timestamp without time zone, t2 timestamp with time zone);
    insert into a(t) values (&#39;2012-03-01&#39;::timestamp);
    update a set t2 = t;
    select * from a;
              t          |           t2           
    ---------------------+------------------------
     2012-03-01 00:00:00 | 2012-03-01 00:00:00-08

    alter table a alter column t type timestamp with time zone;
    select * from a;
               t            |           t2           
    ------------------------+------------------------
     2012-03-01 00:00:00-08 | 2012-03-01 00:00:00-08

According to the manual for [Alter Table][1]:

&gt; if *[the USING clause is]* omitted, the default conversion is the same as an assignment cast from old data type to new.

According to the manual for [Date/Time types][2]
&gt; Conversions between *timestamp without time zone* and *timestamp with time zone* normally assume that the *timestamp without time zone* value should be taken or given as *timezone* local time. A different time zone can be specified for the conversion using `AT TIME ZONE`.


  [1]: http://www.postgresql.org/docs/current/static/sql-altertable.html
  [2]: http://www.postgresql.org/docs/current/static/datatype-datetime.html

It is better to specify the time zone explicitly. Say, if your timestamp are supposed to be in **UTC** (but without timezone), you should be wary of the fact that the timezone of the client or server might be messing everything here. Instead write:

    ALTER TABLE a ALTER COLUMN t TYPE TIMESTAMP WITH TIME ZONE USING t AT TIME ZONE &#39;UTC&#39;

I would like to execute a number of `bash` commands from a `Rakefile`.

I have tried the following in my `Rakefile` 

    task :hello do
      %{echo &quot;World!&quot;}
    end

but upon executing `rake hello` there is no output?
How do I execute bash commands from a Rakefile?


**NOTE**:This is not a duplicate as it&#39;s specifically asking how to execute bash commands from a _Rakefile_.

Execute bash commands from a Rakefile

TCP has the tuple pairs (IP Addr/port/type) to tell one client from another.  UDP passes the client IP and port.  How does the unix domain keep track of different clients?

In other words the server creates a socket bound to some path say /tmp/socket.  2 or more clients connect to /tmp/socket.  What is going on underneath that keeps track of data from client1 and client2?  I imagine the network stack plays no part in domain sockets so is the kernel doing all the work here?

Is there a unix domain protocol format like there is an IP protocol format and TCP/UDP formats?  Is the format of domain socket datagram protocols published somewhere?  Is every unix different or does something like POSIX standardize it?

Thanks for any illumination.  I could not find any information that explained this.  Every source just glossed over how to use the domain sockets.

How do Unix Domain Sockets differentiate between multiple clients?

The question is short: if I already have data in a column type timestamp without time zone, if I set the type to timestamp with time zone, what does postgresql do with this data?

PostgreSQL alter type timestamp without time zone -&gt; with time zone

<p>The question is short: if I already have data in a column type timestamp without time zone, if I set the type to timestamp with time zone, what does postgresql do with this data?</p>


In plpgsql, I want to get the array contents one by one from a two dimension array.

    DECLARE
      m varchar[];
      arr varchar[][] := array[[&#39;key1&#39;,&#39;val1&#39;],[&#39;key2&#39;,&#39;val2&#39;]];
    BEGIN
      for m in select arr
      LOOP
        raise NOTICE &#39;%&#39;,m;
      END LOOP;
    END;

But the above code returns:

    {{key1,val1},{key2,val2}}

in one line. I want to be able to loop over and call another function which takes parameters like:

    another_func(key1,val1)

Loop over array dimension in plpgsql

I believe the title is self-explanatory. How do you create the table structure in  PostgreSQL to make a many-to-many relationship.

My example:

    Product(name, price);
    Bill(name, date, Products);

How to implement a many-to-many relationship in PostgreSQL?

I want to run this query:

    SELECT DISTINCT ON (address_id) purchases.address_id, purchases.*
    FROM purchases
    WHERE purchases.product_id = 1
    ORDER BY purchases.purchased_at DESC

But I get this error:

&gt; PG::Error: ERROR:  SELECT DISTINCT ON expressions must match initial ORDER BY expressions

Adding `address_id` as first `ORDER BY` expression silences the error, but I really don&#39;t want to add sorting over `address_id`. Is it possible to do without ordering by `address_id`?

PostgreSQL DISTINCT ON with different ORDER BY

I tried the following select:

    SELECT (id,name) FROM v_groups vg 
    inner join people2v_groups p2vg on vg.id = p2vg.v_group_id
    where p2vg.people_id =0;

and I get the following error column reference `id` is ambiguous.

Thing is if I try the same `SELECT` but I only ask for `name`, and not for `id` also, it works.
I&#39;m new to this and maybe I am missing something obvious. Any suggestions? 

Thanks.

Postgresql column reference &quot;id&quot; is ambiguous

I do not understand what is wrong with this query? Query tool does not want to create a table in PostgreSQL.

    CREATE TABLE article (
    article_id bigint(20) NOT NULL auto_increment,
    article_name varchar(20) NOT NULL,
    article_desc text NOT NULL,
    date_added datetime default NULL,
    PRIMARY KEY (article_id)
    );



create table in postgreSQL

I know how to get the timezone offset, but what I need is the ability to detect something like &quot;America/New York.&quot; Is that even possible from JavaScript or is that something I am going to have to guestimate based on the offset?

How can I get the timezone name in JavaScript?

Can somebody please tell, what&#39;s the difference between the following two statements:

    TimeZone.getTimeZone(&quot;America/New_York&quot;)

and

    TimeZone.getTimeZone(&quot;EST&quot;)

In other words, why is EST different from America/New_York. Also in my application, to get the current time zone in US, should I use America/New_York or EST.



Difference between EST and America/New_York time zones

I am looking for a function to convert date in one timezone to another. 

It need two parameters, 

 - date (in format &quot;2012/04/10 10:10:30 +0000&quot;) 
 - timezone string (&quot;Asia/Jakarta&quot;)

The timezone string is described in http://en.wikipedia.org/wiki/Zone.tab

Is there an easy way to do this?

Convert date to another timezone in JavaScript

I have to print the EST time in my Java application. I had set the time zone to EST using:

    Calendar cal = Calendar.getInstance(TimeZone.getTimeZone(&quot;EST&quot;));

But when the daylight savings is being followed in this timezone, my code does not print the correct time (it prints 1 hour less).

How to make the code work to read the correct time always, irrespective of whether the daylight savings are being observed or not?

PS: I tried setting the timezone to EDT, but it doesn&#39;t solve the problem.


How to tackle daylight savings using TimeZone in Java

I am in the process of migrating an application from django 1.2 To 1.4.

I have a daily task object which contains a time of day that task should be completed:

    class DailyTask(models.Model):
        time = models.TimeField()
        last_completed = models.DateTimeField()
        name = models.CharField(max_length=100)
        description = models.CharField(max_length=1000)
        weekends = models.BooleanField()
        
        def __unicode__(self):
            return &#39;%s&#39; % (self.name)
            
        class Meta:
            db_table = u&#39;dailytask&#39;
            ordering = [&#39;name&#39;]

In order to check if a task is still required to be completed today, I have the following code:

    def getDueDailyTasks():
        dueDailyTasks=[]
        now = datetime.datetime.now()
        try:
            dailyTasks = DailyTask.objects.all()
        except dailyTask.DoesNotExist:
            return None
        for dailyTask in dailyTasks:
            timeDue = datetime.datetime(now.year,now.month,now.day,dailyTask.time.hour,dailyTask.time.minute,dailyTask.time.second)
            if timeDue&lt;now and timeDue&gt;dailyTask.last_completed:
                if dailyTask.weekends==False and now.weekday()&gt;4:
                    pass
                else:
                    dueDailyTasks.append({&#39;id&#39;:dailyTask.id,
                                &#39;due&#39;:timeDue,
                                 &#39;name&#39;: dailyTask.name,
                                 &#39;description&#39;:dailyTask.description})
        return dueDailyTasks

This worked fine under 1.2, But under 1.4 I get the error:

    can&#39;t compare offset-naive and offset-aware datetimes

due to the line

    if timeDue&lt;now and timeDue&gt;dailyTask.last_completed

and both comparison clauses throw this error.

I have tried making timeDue timezone aware by adding pytz.UTC as an argument, but this still raises the same error.

I&#39;ve read some of the docs on timezones but am confused as to whether I just need to make timeDue timezone aware, or whether I need to make a fundamental change to my db and existing data.

Content Type	Original Author	Original Content on Stackoverflow
Question	gyorgyabraham	View Question on Stackoverflow
Solution 1 - Postgresql	dbenhur	View Answer on Stackoverflow
Solution 2 - Postgresql	Antti Haapala -- Слава Україні	View Answer on Stackoverflow

PostgreSQL alter type timestamp without time zone -> with time zone

Postgresql Problem Overview

Postgresql Solutions

Solution 1 - Postgresql

Solution 2 - Postgresql

How do Unix Domain Sockets differentiate between multiple clients?

Execute bash commands from a Rakefile

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