Question

I have table consisting of these fields:

id  |   date_from  | date_to      |   price   |  status
----------------------------------------------------------
CK1     22-12-2012   29-12-2012       800         1
CK1     22-12-2012   29-12-2012       1200        1
CK2     24-12-2012   30-12-2012       1400        0
CK2     24-12-2012   30-12-2012       1800        1
CK2     24-12-2012   30-12-2012       2200        1

How do I create SQL select that groups results by ID, DATE_FROM, DATE_TO and picks lowest value from price where status == 1 and also to count amount of how many records where grouped?

So result would be

id    | date_from   | date_to      |   price   |  count
CK1     22-12-2012    29-12-2012       800        2
CK2     24-12-2012    30-12-2012       1800       2

And maybe, is there a way to find out how many of records were not grouped because of status == 0? This is not very important, I am just wondering whether there is a way how to find out number of uncounted records for group of records.

Answer 1

Your description doesn’t match what you want the result to be.

This will match your description, i.e. give you the lowest price where status is 1, and count the number of records in the group:

select id, date_from, date_to, min(case status when 1 then price end) as price, count(*) as count
from TheTable
group by id, date_from, date_to

Result:

id    | date_from   | date_to      |   price   |  count
CK1     22-12-2012    29-12-2012       800        2
CK2     24-12-2012    30-12-2012       1800       3

This will give you the result that you asked for, i.e. filter out the records where status is 1, get you the lowest price, and get the number of records in the groups after filtering:

select id, date_from, date_to, min(price) as price, count(*) as count
from TheTable
where status = 1
group by id, date_from, date_to

Result:

id    | date_from   | date_to      |   price   |  count
CK1     22-12-2012    29-12-2012       800        2
CK2     24-12-2012    30-12-2012       1800       2

---

To get the number of records where the status is 0, you need to use the first method, where you don’t filter out those records. If the status only can be 0 or 1, you can simply use sum(status) to get the number of records where the status is 1, and count(case status when 0 then 1 end) or sum(1 - status) to get the number of records where the status is 0.