Create a third row that make the sum of past row + current row (i.e. a running sum)?

Dialect: SQL 92
EXAMPLE :
WEEK TOTAL T
----------- ----------- -----------
3 5 14
2 6 8
1 5 3
0 3 0

Dialect: SQL 92

SQL:

SELECT T2.WEEK, T2.TOTAL, COALESCE(SUM(T1.TOTAL), 0) AS T

FROM MY_TABLE T1

       LEFT OUTER JOIN MY_TABLE T2

             ON T1.WEEK < T2.WEEK

GROUP BY T2.WEEK, T2.TOTAL

ORDER BY 1 DESC

Here I use the COALESCE function that will replace the NULL that can be found in some rows by 0 (otherwise the sum couldn't be done)

Dialect: SQL 99
Nearly the same but last column is current total + previous like :
week total t
1 5 5
2 6 11
3 5 16

SQL:

select t2.week, t2.total, sum(t1.total)

from  MY_TABLE T1,  MY_TABLE T2

 where T1.WEEK <=t2.week

group by  t2.week, T2.total

order by t2.week asc

Dialect: SQL 99
The following feature outside Core SQL-99 is used:

T611, "Elementary OLAP operations"
(checked with the mimer sql validator)

SQL:

SELECT week

     , total

     , sum(total) over (order by week desc) as running_total

FROM my_table