Confrontando record a record precedente in PostgreSQL

Question

Ho una tabella in PostgreSQL DB come questo:

Client | Rate | StartDate|EndDate  
A  | 1000 | 2005-1-1 |2005-12-31 
A  | 2000 | 2006-1-1 |2006-12-31 
A  | 3000 | 2007-1-1 |2007-12-31 
B  | 5000 | 2006-1-1 |2006-12-31 
B  | 8000 | 2008-1-1 |2008-12-31 
C  | 2000 | 2006-1-1 |2006-12-31 

Come ottenere questo risultato?

Client | Rate | StartDate|EndDate |Pre Rate | Pre StartDate |Pre EndDate  
A  | 1000 | 2005-1-1 |2005-12-31 |   |    |    
A  | 2000 | 2006-1-1 |2006-12-31 | 1000 | 2005-1-1  |2005-12-31    
A  | 3000 | 2007-1-1 |2007-12-31 | 2000 | 2006-1-1  |2006-12-31 
B  | 5000 | 2006-1-1 |2006-12-31 |   |    |    
B  | 8000 | 2008-1-1 |2008-12-31 | 5000 | 2006-1-1  |2006-12-31 
C  | 2000 | 2006-1-1 |2006-12-31 

Grazie mille !!!

Answer 1

SELECT client, 
     rate, 
     startdate, 
     enddate, 
     lag(rate) over client_window as pre_rate, 
     lag(startdate) over client_window as pre_startdate, 
     lag(enddate) over client_window as pre_enddate 
FROM the_table 
WINDOW client_window as (partition by client order by startdate) 
ORDER BY client, stardate; 

Questo presuppone che enddate è sempre maggiore startdate dalla stessa riga e che nessun enddate è maggiore della seguente startdate