PostgreSQL 实现累加

exchange=# select invoice_id, client_id , total_amount,invoice_end   from  invoice   order by invoice_id ;
 invoice_id | client_id | total_amount |      invoice_end       
------------+-----------+--------------+------------------------
         31 |         1 |     14.06202 | 2010-12-20 00:00:00+00
         71 |         4 |    -45.25617 | 2010-12-20 00:00:00+00
         75 |         3 |      2.52500 | 2010-12-17 00:00:00+00
         76 |         3 |      9.36850 | 2010-12-18 00:00:00+00
         77 |         3 |     34.40367 | 2010-12-19 00:00:00+00
         78 |         3 |      0.00000 | 2010-12-20 00:00:00+00
(6 rows)

exchange=# 

现在将 total_amount累加

exchange=# select                                                                                         
 invoice.invoice_id, invoice.client_id ,invoice. total_amount,invoice.invoice_end,
 (select sum(total_amount) as past_due from invoice as inner_invoice where client_id = invoice.client_id and inner_invoice.invoice_end <= invoice.invoice_end) as grand_total
 from invoice  order  by invoice.invoice_id;
 invoice_id | client_id | total_amount |      invoice_end       | grand_total 
------------+-----------+--------------+------------------------+-------------
         31 |         1 |     14.06202 | 2010-12-20 00:00:00+00 |    14.06202
         71 |         4 |    -45.25617 | 2010-12-20 00:00:00+00 |   -45.25617
         75 |         3 |      2.52500 | 2010-12-17 00:00:00+00 |     2.52500
         76 |         3 |      9.36850 | 2010-12-18 00:00:00+00 |    11.89350
         77 |         3 |     34.40367 | 2010-12-19 00:00:00+00 |    46.29717
         78 |         3 |      0.00000 | 2010-12-20 00:00:00+00 |    46.29717
(6 rows)

exchange=# 

grand_total为累加的字段