How to generate multiple time series in one sql query?

Question

Here is the database layout. I have a table with sparse sales over time, aggregated per day. If for an item I have 10 sales on the 01-01-2015, I will have an entry, but If I

Answer 1

First you need a table with all dates to fill the blank dates. 100 years of date mean 36,000 rows so no very big. Instead of calculate every time.

allDates:

date_id
s_date

or created calculating the fields

date_id
s_date
doy = EXTRACT(DOY FROM s_date)
year = EXTRACT(YEAR FROM s_date)

Your base query will be SQL FIDDLE DEMO:

SELECT           
      AD.year,
      AD.doy,           
      allitems.item_id,
      COALESCE(SUM(ED.sales), 0) as max_sales
FROM 
    (SELECT DISTINCT item_id
     FROM entry_daily 
    ) as allitems
CROSS JOIN alldates AD
LEFT JOIN entry_daily ED
       ON ED.day_of_year = AD.doy
      AND ED.year = AD.year  
      AND ED.item_id = allitems.item_id
WHERE AD.year = 2015
GROUP BY
     AD.year, AD.doy, allitems.item_id
ORDER BY 
     AD.year, AD.doy, allitems.item_id

You will have this OUTPUT

| year | doy | item_id | max_sales |
|------|-----|---------|-----------|
| 2015 |   1 |      A1 |        20 |
| 2015 |   1 |      A2 |        11 |
| 2015 |   2 |      A1 |         0 |
| 2015 |   2 |      A2 |         0 |
| 2015 |   3 |      A1 |         0 |
| 2015 |   3 |      A2 |         0 |
| 2015 |   4 |      A1 |         0 |
| 2015 |   4 |      A2 |         0 |
| 2015 |   5 |      A1 |         0 |
| 2015 |   5 |      A2 |         0 |
| 2015 |   6 |      A1 |         0 |
| 2015 |   6 |      A2 |         0 |
| 2015 |   7 |      A1 |        39 |
| 2015 |   7 |      A2 |         0 |
| 2015 |   8 |      A1 |         0 |
| 2015 |   8 |      A2 |         0 |
| 2015 |   9 |      A1 |         0 |
| 2015 |   9 |      A2 |         0 |
| 2015 |  10 |      A1 |         0 |
| 2015 |  10 |      A2 |         0 |

Then you need install tablefunc

and use crosstab to pivot this table SAMPLE