计算运行总计，每个月保持不变

Question

I need to calculate the running total, would like a constant number for each month, only to have it increase by a specific amount for each succeeding month. However I can't group or partition out the dates to do this... and I only know about the code to write a continuous running total.

I've tried this:

SELECT 
    monthdates,
    sum(10) OVER (
        PARTITION BY monthdates ORDER BY monthdates ASC rows between unbounded preceding and current row)
FROM mytable;

..which is wrong because I want this:

+------------+-----+
| monthdates | sum |
+------------+-----+
| 2018-01-01 |  10 |
| 2018-01-01 |  10 |
| 2018-02-01 |  20 |
| 2018-02-01 |  20 |
| 2018-02-01 |  20 |
| 2018-02-01 |  20 |
| 2018-02-01 |  20 |
| 2018-03-01 |  30 |
| 2018-03-01 |  30 |
+------------+-----+

How do I approach this problem? Thanks in advance!

Answer 1

First get the running sum over the distinct monthdates and then join them to your table on the monthdates .

SELECT t2.monthdates,
       x2.sum
       FROM mytable t2
            INNER JOIN (SELECT x1.monthdates,
                               sum(10) OVER (ORDER BY x1.monthdates) sum
                               FROM (SELECT DISTINCT
                                            t1.monthdates
                                            FROM mytable t1) x1) x2
                       ON x2.monthdates = t2.monthdates
       ORDER BY t2.monthdates;

You could solve it even easier by using dense_rank() multiplied by 10 , but without sum() .

SELECT t1.monthdates,
       dense_rank() OVER (ORDER BY t1.monthdates) * 10 sum
       FROM mytable t1
       ORDER BY t1.monthdates;

db<>fiddle