In SQL Server you can do it like
To get the first number,
SELECT CAST(DATEPART(YEAR,GETDATE()) AS VARCHAR)+'/'+RIGHT('0'+CAST(DATEPART(MONTH,GETDATE()) AS VARCHAR),2)+'/'+RIGHT('0'+CAST(DATEPART(DAY,GETDATE()) AS VARCHAR),2)+'/'+'001'
You can make it dynamic to check with some field of a table to get latest value like
DECLARE @OrderSequenceBase VARCHAR(20)
SELECT @OrderSequenceBase= CAST(DATEPART(YEAR,GETDATE()) AS VARCHAR)+'/'+RIGHT('0'+CAST(DATEPART(MONTH,GETDATE()) AS VARCHAR),2)+'/'+RIGHT('0'+CAST(DATEPART(DAY,GETDATE()) AS VARCHAR),2)+'/'
DECLARE @OrderSequenceTrail VARCHAR(3)
SELECT @OrderSequenceTrail=CASE WHEN OrderSequence LIKE @OrderSequenceBase+'%' THEN ISNULL (RIGHT(OrderSequence,3),'0') ELSE '0' END
FROM YourTable
WHERE OrderSequence LIKE @OrderSequenceBase+'%'
SELECT @OrderSequenceBase+RIGHT('00'+CAST(CAST(@OrderSequenceTrail AS INT)+1 AS VARCHAR),3)
Example:
DECLARE @OrderSequenceBase VARCHAR(20)
SELECT @OrderSequenceBase= CAST(DATEPART(YEAR,GETDATE()) AS VARCHAR)+'/'+RIGHT('0'+CAST(DATEPART(MONTH,GETDATE()) AS VARCHAR),2)+'/'+RIGHT('0'+CAST(DATEPART(DAY,GETDATE()) AS VARCHAR),2)+'/'
DECLARE @OrderSequence VARCHAR(20)
SELECT @OrderSequence='2015/06/25/003'
DECLARE @OrderSequenceTrail VARCHAR(3)
SELECT @OrderSequenceTrail=CASE WHEN @OrderSequence LIKE @OrderSequenceBase+'%' THEN ISNULL (RIGHT(@OrderSequence,3),'0') ELSE '0' END
SELECT @OrderSequenceBase+RIGHT('00'+CAST(CAST(@OrderSequenceTrail AS INT)+1 AS VARCHAR),3)
I have no idea about PostgreSQL but the approach should work.
Hope, it helps :)