Convert Hexadecimals to timestamp in postgres - postgresql

Question

I have the following hexadecimal data that I want to convert using the postgres functions, the data they receive is the following:
#AVLData_TimeStamp #AVLData_GPSElement_Altitude
00000174C0FA7EA0 0140
And I want to convert them to the following data
#MOPO_FECHAHORA #MOPO_ALTITUD
2020-09-24 09:37:56.000 320
I have tried to do it using this function but have not succeeded
SELECT to_timestamp(#AVLData_TimeStamp)
I have two functions in SQLserver that do this but in postgres I don't know how to do it
First Function:
CREATE FUNCTION FUN_Unix_To_Date(
#FechaUnix CHAR(38)
)
RETURNS DATETIME
AS
BEGIN
DECLARE
#LocalTime BIGINT
,#Adjusted BIGINT
,#seconds BIGINT = #FechaUnix
SET #LocalTime = DATEDIFF(MS,GETDATE(),GETUTCDATE())
SET #Adjusted = #seconds - #LocalTime
RETURN (DATEADD(SECOND,CONVERT(BIGINT, LEFT(CAST(#Adjusted AS VARCHAR(100)),13))/1000, CAST('1970-01-01 00:00:00' AS DATETIME)))
END
Two Function:
CREATE FUNCTION HexadecimalToDec_v2(
#hexval CHAR(38)
)
RETURNS NUMERIC(38)
AS
BEGIN
DECLARE #i INT
,#digits INT
,#result NUMERIC
,#current_digit CHAR(1)
,#current_digit_dec NUMERIC
SET #digits = LEN(#hexval)
SET #i = 0
SET #result =0
WHILE #i <= #digits
BEGIN
SET #current_digit = SUBSTRING(#hexval, #i, 1)
IF #current_digit = 'A' OR
#current_digit = 'B' OR
#current_digit = 'C' OR
#current_digit = 'D' OR
#current_digit = 'E' OR
#current_digit = 'F'
SET #current_digit_dec = ASCII(#current_digit) - ASCII('A') + 10
ELSE
SET #current_digit_dec = CONVERT(INT,#current_digit)
SET #result = (#result * 16) + #current_digit_dec
SET #i = #i + 1
END
RETURN(#result)
END
and finally the function is used like this
#MOPO_FECHAHORA = (dbo.Unix_To_Date(dbo.FUN_HexadecimalToDec_v2(#AVLData_TimeStamp)))
And this is the result
#MOPO_FECHAHORA
2020-09-24 09:37:56.000
Thank you very much for your help.

Answer 1

Use the function from this answer to convert hexadecimal to decimal (you might want to use bigint rather than integer):
CREATE OR REPLACE FUNCTION hex_to_int(hexval text) RETURNS bigint
LANGUAGE plpgsql IMMUTABLE STRICT AS
$$DECLARE
result bigint;
BEGIN
EXECUTE 'SELECT x' || quote_literal(hexval) || '::bigint'
INTO result;
RETURN result;
END;$$;
The timestamp can then be converted with
to_timestamp(hex_to_int('00000174C0FA7EA0') / 1000.0)

Answer 2

Just to clarify the source of issue.
The problem is that the your value(s) is the "local" epoch but to_timestamp() function returns timestamp with timezone value. Lets try some example:
with t(x) as (values('2020-09-24 09:37:56'))
select
x::timestamp as srcts,
x::timestamptz as srctstz,
to_timestamp(extract(epoch from x::timestamp)) as cnvts,
to_timestamp(extract(epoch from x::timestamptz)) as cnvtstz
from t;
┌─[ RECORD 1 ]─────────────────────┐
│ srcts │ 2020-09-24 09:37:56 │
│ srctstz │ 2020-09-24 09:37:56+03 │
│ cnvts │ 2020-09-24 12:37:56+03 │ <- Here is the issue in our case
│ cnvtstz │ 2020-09-24 09:37:56+03 │
└─────────┴────────────────────────┘
As you can see the data source type is critical. That's why you got the increased (actually converted from UTC to the local time zone) value in the first try using #LaurenzAlbe answer.
To fix this issue you need to perform some "reverse" calculations:
with t(x) as (values('2020-09-24 09:37:56'))
select
x::timestamp as srcts,
x::timestamptz as srctstz,
to_timestamp(extract(epoch from x::timestamp)) as cnvts,
(to_timestamp(extract(epoch from x::timestamp)))::timestamptz at time zone 'utc' as cnvtsrecalc,
to_timestamp(extract(epoch from x::timestamptz)) as cnvtstz
from t;
┌─[ RECORD 1 ]┬────────────────────────┐
│ srcts │ 2020-09-24 09:37:56 │
│ srctstz │ 2020-09-24 09:37:56+03 │
│ cnvts │ 2020-09-24 12:37:56+03 │ <- Here is the issue in our case
│ cnvtsrecalc │ 2020-09-24 09:37:56 │ <- Issue fixed
│ cnvtstz │ 2020-09-24 09:37:56+03 │
└─────────────┴────────────────────────┘
The following function wraps all this logic including the conversion of the hex value to bigint:
create or replace function hex2ts(text)
returns timestamp
language sql
immutable
strict
as $$
select
(to_timestamp(('x' || lpad($1, 16, '0'))::bit(64)::bigint / 1000.0))::timestamptz at time zone 'utc'
$$;