Find date sequence in PostgreSQL - postgresql

Question

I'm trying to find the maximum sequence of days by customer in my data. I want to understand what is the max sequence of days that specific customer made. If someone enter to my app in the 25/8/16 AND 26/08/16 AND 27/08/16 AND 01/09/16 AND 02/09/16 - The max sequence will be 3 days (25,26,27).
In the end (The output) I want to get two fields: custid | MaxDaySequence
I have the following fields in my data table: custid | orderdate(timestemp)
For exmple:
custid orderdate
1 25/08/2007
1 03/10/2007
1 13/10/2007
1 15/01/2008
1 16/03/2008
1 09/04/2008
2 18/09/2006
2 08/08/2007
2 28/11/2007
2 04/03/2008
3 27/11/2006
3 15/04/2007
3 13/05/2007
3 19/06/2007
3 22/09/2007
3 25/09/2007
3 28/01/2008
I'm using PostgreSQL 2014.
Thanks
Trying:
select custid, max(num_days) as longest
from (
select custid,rn, count (*) as num_days
from (
select custid, date(orderdate),
cast (row_number() over (partition by custid order by date(orderdate)) as varchar(5)) as rn
from table_
) x group by custid, CURRENT_DATE - INTERVAL rn|| ' day'
) y group by custid

Answer 1

Try:
SELECT custid, max( abc ) as max_sequence_of_days
FROM (
SELECT custid, yy, count(*) abc
FROM (
SELECT * ,
SUM( xx ) OVER (partition by custid order by orderdate ) yy
FROM (
select * ,
CASE WHEN
orderdate - lag( orderdate ) over (partition by custid order by orderdate )
<= 1
THEN 0 ELSE 1 END xx
from mytable
) x
) z
GROUP BY custid, yy
) q
GROUP BY custid
Demo: http://sqlfiddle.com/#!15/00422/11
===== EDIT ===========
Got "operator does not exist: interval <= integer"
This means that orderdate column is of type timestamp, not date.
In this case you need to use <= interval '1' day condition instead of <= 1:
Please see this link: https://www.postgresql.org/docs/9.0/static/functions-datetime.html to learn more about date arithmetic in PostgreSQL
Please see this demo:
http://sqlfiddle.com/#!15/7c2200/2
SELECT custid, max( abc ) as max_sequence_of_days
FROM (
SELECT custid, yy, count(*) abc
FROM (
SELECT * ,
SUM( xx ) OVER (partition by custid order by orderdate ) yy
FROM (
select * ,
CASE WHEN
orderdate - lag( orderdate ) over (partition by custid order by orderdate )
<= interval '1' day
THEN 0 ELSE 1 END xx
from mytable
) x
) z
GROUP BY custid, yy
) q
GROUP BY custid