One column as parameter both having and where (excluding) - sql

Question

I have such two queries:
First:
select p.prodid, p.name, max(b.ldate) as lastsale
from prod p, buy b
where p.id = b.idprod and b.id<>0 and b.wskus=0 and b.bufor=0
group by p.prodid, p.name
HAVING sum(b.curNo)=0
order by p.name asc
Second
select p.prodid, p.name, min(b.buydate) as oldest_buy
from prod p, buy b
where p.id = b.idprod and b.id<>0 and b.wskus=0 and b.bufor=0 and b.curNo>0
group by p.prodid, p.name
order by p.name asc
How can I make JOIN for them to have as a result columns:
| p.prodid | p.name | lastsale | oldest_buy |
| 1 | ex1 | 1.1.18 | NULL |
| 2 | ex2 | NULL | 1.1.18 |
as HAVING sum(b.curNo)=0 from first query is exclusive to WHERE parameter from second query b.curNo>0 I have problem how to make this work.

Answer 1

Without your input data it's hard to tell, but it's possible this will work for you...
SELECT
p.prodid,
p.name,
MIN(CASE WHEN b.curNo > 0 THEN b.buydate END) AS oldest_buy, -- MIN(buydate) WHERE curno>0
CASE WHEN SUM(b.curNo) = 0 THEN MAX(b.ldate) END AS lastsale -- MAX(ldate) HAVING SUM(curNo) = 0
FROM
prod p
INNER JOIN -- Don't use "," use "JOIN"s, the standard for about 25 years...
buy b
ON p.id = b.idprod
WHERE
b.id <> 0
AND b.wskus = 0
AND b.bufor = 0
GROUP BY
p.prodid,
p.name
ORDER BY
p.name ASC
It's possible that moving the b.curNo > 0 or the SUM(b.curNo) = 0 in to the CASE statements will give extra rows, depending on the behavior of your data. It's impossible to tell without more details or example data.
The values in the two calculations will be okay, but I can't speak for the number of rows.
To be more explicit about it you could do...
SELECT
p.prodid,
p.name,
CASE WHEN MAX(b.curNo) > 0 THEN MIN(CASE WHEN b.curNo > 0 THEN b.buydate END) END AS oldest_buy,
CASE WHEN SUM(b.curNo) = 0 THEN MAX(b.ldate) END AS lastsale
FROM
prod p
INNER JOIN -- Don't use "," use "JOIN"s, the standard for about 25 years...
buy b
ON p.id = b.idprod
WHERE
b.id <> 0
AND b.wskus = 0
AND b.bufor = 0
GROUP BY
p.prodid,
p.name
HAVING
SUM(b.curNo) = 0
OR MAX(b.curNo) > 0
ORDER BY
p.name ASC
Another possibility (Again because you didn't give example data) is to aggregate then join.
This is based on the notion that you mean p.curNo rather than b.curNo...
SELECT
p.prodid,
p.name,
CASE p.curNo > 0 THEN b.oldest_buy END AS oldest_buy,
CASE p.curNo = 0 THEN b.last_sale END AS lastsale
FROM
prod p
INNER JOIN -- Don't use "," use "JOIN"s, the standard for about 25 years...
(
SELECT
idprod,
MIN(buydate) AS oldest_buy,
MAX(ldate) AS last_sale
FROM
buy
WHERE
b.id <> 0
AND b.wskus = 0
AND b.bufor = 0
)
b
ON p.id = b.idprod
ORDER BY
p.name ASC

Answer 2

Put the first query in a subquery before union all. Try this:
select
t.prodid, t.name, t.lastsale, null as oldest_buy
from (select p.prodid, p.name,
max(b.ldate) as lastsale
from prod p, buy b
where p.id = b.idprod and b.id<>0 and
b.wskus=0 and b.bufor=0
group by p.prodid, p.name
HAVING sum(b.curNo)=0 ) t
union all
( select p.prodid, p.name,
null as lastsale, min(b.buydate) as oldest_buy
from prod p, buy b
where p.id = b.idprod and b.id<>0 and b.wskus=0
and b.bufor=0 and b.curNo>0
group by p.prodid, p.name )
order by 2 asc