mysql - conditionals with joins - only distinct rows - mysql

Question

Sorry for not precise subject. More precise description is here:
Consider example tables:
City:
cityId | cityName
----------------------
51 | NY
52 | Chicago
53 | SanFrancisco
People:
peopleId | peopleName |
-----------------------
21 | John |
22 | Emma |
23 | Frank |
24 | George |
25 | Albert |
Goods:
goodsId | good | peopleId | cityId
------------------------------------
1 | bread | 21 | 51
2 | steel | 22 | 51
3 | onion | 23 | 0
4 | chair | 22 | 52
5 | knife | 22 | 0
Input data:
cityId: 51
peopleId: (21, 22, 23, 25)
Expected result:
peopleId | peopleName | cityId | cityName | goodId | good
-----------------------------------------------------------
21 | John | 51 | NY | 1 | bread
22 | Emma | 51 | NY | 2 | steel
23 | Frank | 0 | --- | 3 | onion
25 | Albert | --- | --- | --- | ----
22 | Emma | 0 | --- | 5 | knife
Even if there is almost empty data still some row is displayed (here peopleId 25). What is going on here?
I want to select all the goods.good that have people.peopleId in input data (21, 22, 23, 25) and cityId = 51. However not every row in goods table have specified goods.cityId, and also not every goods.peopleId is in goods table. I want my result to be conditionally dependent:
if peopleId exists in goods table and this row have also cityId i am looking - print it.
else if peopleId exists in goods table but goods.cityId = 0 - select it.
else if peopleId doesnt exist in goods table - print only peopleId and peopleName, rest of the fields leave empty.
I already made this:
SELECT DISTINCT people.peopleId, people.peopleName,
CASE
WHEN goods.cityId = 51
THEN (SELECT goods.good FROM goods WHERE goods.zalozenie = 51 AND goods.peopleId = people.peopleId)
ELSE
CASE
WHEN goods.cityId = 0
THEN (SELECT goods.good FROM goods WHERE goods.cityId = 0 AND goods.peopleId = people.peopleId)
ELSE -1
END
END AS goods FROM people LEFT JOIN goods ON people.peopleId = goods.peopleId WHERE people.peopleId IN ( 21, 22, 23, 25 )
This works almost fine but result shows:
peopleId | peopleName | cityId | cityName | goodId | good
-----------------------------------------------------------
21 | John | 51 | NY | 1 | bread
22 | Emma | 51 | NY | 2 | steel
23 | Frank | 0 | --- | 3 | onion
25 | Albert | --- | --- | --- | ----
22 | Emma | 0 | --- | 5 | knife
Unwanted row is the last one - it should only select second line and ignore last one if peopleId = 22 with cityId > 0 is already on result.
Hope you can help me!
Kalreg

Answer 1

I think you are trying to do something like this:
SELECT p.peopleId, p.peopleName, c.cityId, c.cityName, g.goodId, g.good
FROM people p left join goods g
on p.peopleId = g.peopleId
left join city c
on c.cityId = g.cityId
WHERE
(g.goodId is null or g.cityId = 51 or (g.cityId = 0 and NOT EXISTS (SELECT * FROM goods g2 WHERE g2.peopleId=p.peopleId and g2.cityId>0)))
and p.peopleId IN (21, 22, 23, 25);
See this sql fiddle to play around with it a bit. Hopefully that's a starting point, anyway.