Question

I have a few issues doing a typical report style SQL that I’m hoping someone with more experience might be able to help with.

I have the following tables

products

• product_id
• product_name
• product_category

product_defects

• product_id
• defect_date
• high_priority
• med_priority
• low_priority

calendar

• date

And what I want is to be able to generate a report that outlines the number of high / medium / low defects associated with each product category on each day e.g – even though data may not exist in product_defect for a particular day, in which case it should be returned as 0. Example:

product_category | date | high | medium | low

1 2012-10-01 1 5 6

2 2012-10-01 2 4 3

3 2012-10-01 1 5 6

1 2012-10-02 0 0 0

2 2012-10-02 2 4 3

3 2012-10-02 1 5 6

…

What I’ve done so far is:

• Create a lookup table called calendar which has a series of days in it going back/forward several years
• Right joined the lookup/product_defects table to get a series of dates so missing days can be marked as 0
• Used COALESCE and SUM to calculate totals and change any missing data to 0
• Used MIN / MAX on the defect_date to get the exact report range

I’ve banged my head on this for a few days now, hoping someone can help.

Thank you

Answer 1

You need to start with all combinations of products and dates, and then join in the defects:

select p.product_category, c.date, 
       coalesce(SUM(high_priority), 0) as high_priority,
       coalesce(SUM(med_priority), 0) as med_priority,
       coalesce(SUM(low_priority), 0) as low_priority
from product p cross join
     calendar c left outer join
     product_defects pd
     on pd.product_id = p.product_id and
        pd.date = c.date
group by p.product_category, c.date
order by 2, 1

(Note: this is untested, so may have syntax errors.)