Обсуждение: Conversion from Number to Date

> On Jun 15, 2023, at 8:23 PM, M Sarwar <sarwarmd02@outlook.com> wrote:
>
> During the data load from CSV files to the database, the above START_TIME and STOP_TIME date column data arrived as
numbervalue. 
> Now I need  to translate the START_TIME and STOP_TIME back to DATE format.

Add a number to a date, you get a date that many days out. Similarly, you can add an interval to a timestamp. So you'll
needto know the base used for those numbers, and the unit of measurement. 

For instance, if the numbers for date are an offset from 1970-01-01 (Unix epoch):

'1970-01-01'::date + <number>

If the numbers for time are seconds from then:

'1970-01-01'::timestamptz + '<number> seconds'::interval

Of course you'll also need to know what time zone the times are in, I will graciously leave that as an exercise ;-)

Also, the documentation page you needed:

https://www.postgresql.org/docs/15/functions-datetime.html

On 6/15/23 21:29, Scott Ribe wrote:
>> On Jun 15, 2023, at 8:23 PM, M Sarwar <sarwarmd02@outlook.com> wrote:
>>
>> During the data load from CSV files to the database, the above START_TIME and STOP_TIME date column data arrived as
numbervalue.
 
>> Now I need  to translate the START_TIME and STOP_TIME back to DATE format.
> Add a number to a date, you get a date that many days out. Similarly, you can add an interval to a timestamp. So
you'llneed to know the base used for those numbers, and the unit of measurement.
 
>
> For instance, if the numbers for date are an offset from 1970-01-01 (Unix epoch):
>
> '1970-01-01'::date + <number>

That was my first thought, but there are only 19500 days since 1 jan 1970.

It turns out that 15 Oct 1900 was 44800 days before today, so 1 Jan 1900 
might be the epoch.

> If the numbers for time are seconds from then:
>
> '1970-01-01'::timestamptz + '<number> seconds'::interval
>
> Of course you'll also need to know what time zone the times are in, I will graciously leave that as an exercise ;-)
>
> Also, the documentation page you needed:
>
> https://www.postgresql.org/docs/15/functions-datetime.html
>
>
>

-- 
Born in Arizona, moved to Babylonia.

On Jun 15, 2023, at 10:23 PM, M Sarwar <sarwarmd02@outlook.com> wrote:
> Output:
> 478         "44795.7306776851"       "44795.731708"                 44795.73067768510         44795.73170800000
> 479         "44795.58143"                   "44795.58246"                   44795.58143000000
44795.58246000000
> 480         "44795.5714184259"       "44795.572495"                 44795.57141842590         44795.57249500000
>
> During the data load from CSV files to the database, the above START_TIME and STOP_TIME date column data arrived as
numbervalue. 
> Now I need  to translate the START_TIME and STOP_TIME back to DATE format.
>
> I am unable to find any documentation or help from the internet.
>
> Does it make sense or did I mess up something?

Where did your CSV files come from? Just guessing, but those look like Modified Julian Dates (MJD). See
https://en.wikipedia.org/wiki/Julian_day#Variants
44795.731708 MJD corresponds to 1981-07-10 17:33:39 UTC. Is that the era your data is from?

If you add 2400000.5 to an MJD value, you get the Julian Date (JD).

If you then subtract 2440587.5 and multiply the result by 86400, you get Unix time (the number of seconds since January
1,1970), excluding leap seconds. 

Putting those together means, if you subtract 40587 from those numbers and multiply by 86400 and then use the
PostgreSQLfunction to_timestamp(), you can convert them to timestamps. 

# SET timezone='utc';
SET
# SELECT to_timestamp((44795.731708 - 40587.0)*86400);
        to_timestamp
-----------------------------
 1981-07-10 17:33:39.5712+00
(1 row)

Again, I'm just guessing as to what your START_TIME and STOP_TIME values mean. You should ask whomever gave you the CSV
files.

Hope this helps,
Ed

P {margin-top:0;margin-bottom:0;}

Hi Ed,

My dates are from the year 2022.

Thanks,

Sarwar

---

From: Ed Sabol <edwardjsabol@gmail.com>
Sent: Friday, June 16, 2023 12:19 AM
To: Pgsql-admin <pgsql-admin@lists.postgresql.org>
Cc: M Sarwar <sarwarmd02@outlook.com>
Subject: Re: Conversion from Number to Date

 

On Jun 15, 2023, at 10:23 PM, M Sarwar <sarwarmd02@outlook.com> wrote:
> Output:
> 478         "44795.7306776851"       "44795.731708"                 44795.73067768510         44795.73170800000
> 479         "44795.58143"                   "44795.58246"                   44795.58143000000         44795.58246000000
> 480         "44795.5714184259"       "44795.572495"                 44795.57141842590         44795.57249500000
> 
> During the data load from CSV files to the database, the above START_TIME and STOP_TIME date column data arrived as number value.
> Now I need  to translate the START_TIME and STOP_TIME back to DATE format.
>
> I am unable to find any documentation or help from the internet.
> 
> Does it make sense or did I mess up something?

Where did your CSV files come from? Just guessing, but those look like Modified Julian Dates (MJD). See https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FJulian_day%23Variants&data=05%7C01%7C%7Cac9d24caf0e04fc41a5c08db6e20ee68%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638224859933137067%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=oEqi9djHFoDxXIcEL7KPr%2BoA2GywVUb1uli7l5nEpz4%3D&reserved=0
44795.731708 MJD corresponds to 1981-07-10 17:33:39 UTC. Is that the era your data is from?

If you add 2400000.5 to an MJD value, you get the Julian Date (JD).

If you then subtract 2440587.5 and multiply the result by 86400, you get Unix time (the number of seconds since January 1, 1970), excluding leap seconds.

Putting those together means, if you subtract 40587 from those numbers and multiply by 86400 and then use the PostgreSQL function to_timestamp(), you can convert them to timestamps.

# SET timezone='utc';
SET
# SELECT to_timestamp((44795.731708 - 40587.0)*86400);
        to_timestamp        
-----------------------------
 1981-07-10 17:33:39.5712+00
(1 row)

Again, I'm just guessing as to what your START_TIME and STOP_TIME values mean. You should ask whomever gave you the CSV files.

Hope this helps,
Ed

P {margin-top:0;margin-bottom:0;}

Hi Ron,

I appreciate your response.

select  to_timestamp((( start_time::numeric (20, 11)) - 25567.0 ) * 86400)

FROM  bronx.test_part_details_all_mcmz_4_cols

limit 24

 

When I try the above, I am getting a difference of 2 days.

 

1 day could be due leap year 1900 discrepancy but I am unable to figure out the additional 1 day difference.

Thanks,

Sarwar

---

From: Ron <ronljohnsonjr@gmail.com>
Sent: Friday, June 16, 2023 1:14 AM
To: pgsql-admin@lists.postgresql.org <pgsql-admin@lists.postgresql.org>
Subject: Re: Conversion from Number to Date

 

Try using the epoch "1 Jan 1900".  An offset of 25567.0 should adjust the date by 70 years.

postgres=# SELECT to_timestamp((44795.731708-25567.0)*86400);
        to_timestamp         
-----------------------------
 2022-08-24 12:33:39.5712-05
(1 row)

You'll have to jigger with time zones yourself.

On 6/15/23 23:53, M Sarwar wrote:

p {margin-top:0; margin-bottom:0}

Hi Ed,

My dates are from the year 2022.

Thanks,

Sarwar

---

From: Ed Sabol <edwardjsabol@gmail.com>
Sent: Friday, June 16, 2023 12:19 AM
To: Pgsql-admin <pgsql-admin@lists.postgresql.org>
Cc: M Sarwar <sarwarmd02@outlook.com>
Subject: Re: Conversion from Number to Date

 

On Jun 15, 2023, at 10:23 PM, M Sarwar <sarwarmd02@outlook.com> wrote:
> Output:
> 478         "44795.7306776851"       "44795.731708"                 44795.73067768510         44795.73170800000
> 479         "44795.58143"                   "44795.58246"                   44795.58143000000         44795.58246000000
> 480         "44795.5714184259"       "44795.572495"                 44795.57141842590         44795.57249500000
> 
> During the data load from CSV files to the database, the above START_TIME and STOP_TIME date column data arrived as number value.
> Now I need  to translate the START_TIME and STOP_TIME back to DATE format.
>
> I am unable to find any documentation or help from the internet.
> 
> Does it make sense or did I mess up something?

Where did your CSV files come from? Just guessing, but those look like Modified Julian Dates (MJD). See https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FJulian_day%23Variants&data=05%7C01%7C%7Cac9d24caf0e04fc41a5c08db6e20ee68%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638224859933137067%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=oEqi9djHFoDxXIcEL7KPr%2BoA2GywVUb1uli7l5nEpz4%3D&reserved=0
44795.731708 MJD corresponds to 1981-07-10 17:33:39 UTC. Is that the era your data is from?

If you add 2400000.5 to an MJD value, you get the Julian Date (JD).

If you then subtract 2440587.5 and multiply the result by 86400, you get Unix time (the number of seconds since January 1, 1970), excluding leap seconds.

Putting those together means, if you subtract 40587 from those numbers and multiply by 86400 and then use the PostgreSQL function to_timestamp(), you can convert them to timestamps.

# SET timezone='utc';
SET
# SELECT to_timestamp((44795.731708 - 40587.0)*86400);
        to_timestamp        
-----------------------------
 1981-07-10 17:33:39.5712+00
(1 row)

Again, I'm just guessing as to what your START_TIME and STOP_TIME values mean. You should ask whomever gave you the CSV files.

Hope this helps,
Ed

--
Born in Arizona, moved to Babylonia.