Convert a string representing a timestamp to an actual timestamp in PostgreSQL? - postgresql

Question

In PostgreSQL: I convert string to timestamp with to_timestamp():
select * from ms_secondaryhealthcarearea
where to_timestamp((COALESCE(update_datetime, '19900101010101'),'YYYYMMDDHH24MISS')
> to_timestamp('20121128191843','YYYYMMDDHH24MISS')
But I get this error:
ERROR: syntax error at end of input
LINE 1: ...H24MISS') >to_timestamp('20121128191843','YYYYMMDDHH24MISS')
^
********** Error **********
ERROR: syntax error at end of input
SQL state: 42601
Character: 176
Why? How to convert a string to timestamp?

Answer 1

One too many opening brackets. Try this:
select *
from ms_secondaryhealthcarearea
where to_timestamp(COALESCE(update_datetime, '19900101010101'),'YYYYMMDDHH24MISS') >to_timestamp('20121128191843','YYYYMMDDHH24MISS')
You had two opening brackets at to_timestamp:
where to_timestamp((COA.. -- <-- the second one is not needed!

Answer 2

#ppeterka has pointed out the syntax error.
The more pressing question is: Why store timestamp data as string to begin with? If your circumstances allow, consider converting the column to its proper type:
ALTER TABLE ms_secondaryhealthcarearea
ALTER COLUMN update_datetime TYPE timestamp
USING to_timestamp(update_datetime,'YYYYMMDDHH24MISS');
Or use timestamptz - depending on your requirements.

Answer 3

Another way to convert a string to a timestamp type of PostgreSql is the above,
SELECT to_timestamp('23-11-1986 06:30:00', 'DD-MM-YYYY hh24:mi:ss')::timestamp without time zone;

Answer 4

I had the same requirement as how I read the title. How to convert an epoch timestamp as text to a real timestamp. In my case I extracted one from a json object. So I ended up with a timestamp as text with milliseconds
'1528446110978' (GMT: Friday, June 8, 2018 8:21:50.978 AM)
This is what I tried. Just the latter (ts_ok_with_ms) is exactly right.
SELECT
data->>'expiration' AS expiration,
pg_typeof(data->>'expiration'),
-- to_timestamp(data->>'expiration'), < ERROR: function to_timestamp(text) does not exist
to_timestamp(
(data->>'expiration')::int8
) AS ts_wrong,
to_timestamp(
LEFT(
data->>'expiration',
10
)::int8
) AS ts_ok,
to_timestamp(
LEFT(
data->>'expiration',
10
)::int8
) + (
CASE
WHEN LENGTH(data->>'expiration') = 13
THEN RIGHT(data->>'expiration', 3) ELSE '0'
END||' ms')::interval AS ts_ok_with_ms
FROM (
SELECT '{"expiration": 1528446110978}'::json AS data
) dummy
This is the (transposed) record that is returned:
expiration 1528446110978
pg_typeof text
ts_wrong 50404-07-12 12:09:37.999872+00
ts_ok 2018-06-08 08:21:50+00
ts_ok_with_ms 2018-06-08 08:21:50.978+00
I'm sure I overlooked a simpler version of how to get from a timestamp string in a json object to a real timestamp with ms (ts_ok_with_ms), but I hope this helps nonetheless.
Update: Here's a function for your convenience.
CREATE OR REPLACE FUNCTION data.timestamp_from_text(ts text)
RETURNS timestamptz
LANGUAGE SQL AS
$$
SELECT to_timestamp(LEFT(ts, 10)::int8) +
(
CASE
WHEN LENGTH(ts) = 13
THEN RIGHT(ts, 3) ELSE '0'
END||' ms'
)::interval
$$;