Increment value colum by previous row in select sql statement - sql

Question

i have to find a way to solve this issue... in a table like that, i would see my column "C" increment his value on each rows, starting from a costant, adding value in column "B" and adding value by the previous value in the same column "C".
Furthermore ... Grouping by User.
For example: (starting point Phil: 350, starting point Mark: 100)
USER - POINT - INITIALPOINT
Phil - 1000 - 1350
Phil - 150 - 1500
Phil - 200 - 1700
Mark - 300 - 400
Mark - 250 - 650
How can i do that?

Answer 1

Using windowing. The table declaration is SQL Server but the rest is standard SQL if your RDBMS supports it (SQL Server 2012, PostgreSQL 9.1 etc)
DECLARE #t TABLE (ID int IDENTITY(1,1), UserName varchar(100), Point int);
INSERT #t (UserName, Point)
VALUES
('Phil', 1000),
('Phil', 150),
('Phil', 200),
('Mark', 300),
('Mark', 250);
DECLARE #n TABLE (UserName varchar(100), StartPoint int);
INSERT #n (UserName, StartPoint)
VALUES
('Phil', 350),
('Mark', 100);
SELECT
T.ID, T.UserName, T.Point,
N.StartPoint + SUM(Point) OVER(PARTITION BY T.UserName ORDER BY T.ID ROWS UNBOUNDED PRECEDING)
FROM
#n N
JOIN
#t T ON N.UserName = T.UserName
ORDER BY
T.ID;
To do this, you need an order to the table (I used ID) and a better way of doing a starting value (I used a separate table)

Answer 2

SQL Server 2008 doesn't support cumulative sums directly using window functions. You can use a correlated subquery for the same effect.
So, using the same structure as GBN:
DECLARE #t TABLE (ID int IDENTITY(1,1), UserName varchar(100), Point int);
INSERT #t (UserName, Point)
VALUES
('Phil', 1000),
('Phil', 150),
('Phil', 200),
('Mark', 300),
('Mark', 250);
DECLARE #n TABLE (UserName varchar(100), StartPoint int);
INSERT #n (UserName, StartPoint)
VALUES
('Phil', 350),
('Mark', 100);
SELECT
T.ID, T.UserName, T.Point,
(N.StartPoint +
(select SUM(Point) from #t t2 where t2.UserName = t.userName and t2.ID <= t.id)
)
FROM
#n N
JOIN
#t T ON N.UserName = T.UserName
ORDER BY
T.ID;

Answer 3

You didn't specify your DBMS, so this is ANSI SQL:
select "user",
point,
case
when "user" = 'Phil' then 350
else 100
end + sum(point) over (partition by "user" order by some_date_column) as sum
from the_table
where "user" in ('Mark', 'Phil')
order by "user", some_date_column;
You need some column to sort the rows by, otherwise the "running sum" will be meaningliss as rows in a table are not sorted (there is no such thing as "the first row" in a relational table). That's the some_date_column is for in my example. It could be an increasing primary key or something else as long as it defines a proper ordering of the rows.