SUM and Group by Logical issue in mysql

Question

I have three tables

City(Id,CityName)
Malls(Id,MallName,CityId)
Stores(Id,StoreName,MallId)

What i want is:

1 = I want to find SUM of all stores in side each city

2= Find SUM of stores in each city if CityId IN(1,2,3,5)

3= Find SUM of stores in each city AS OTHERS if CityId IN(4,6,7,8)

I tried this but can not go further

select count(id) FROM Stores AS s ,Malls AS m,City AS c where s.mallid=m.id and m.cityid=c.id GROUP BY c.id

Answer 1

Stores count in each city:

SELECT c.CityName, COUNT(c.id) AS StoresInCity
FROM Stores s
INNER JOIN Malls m ON s.mallid = m.id
INNER JOIN City c ON m.cityid = c.id
GROUP BY c.CityName

Stores count in each city where CityId IN(1, 2, 3, 5):

SELECT c.CityName, COUNT(c.id) AS StoresInCity
FROM Stores s
INNER JOIN Malls m ON s.mallid = m.id
INNER JOIN City c ON m.cityid = c.id
WHERE m.CityId IN (1, 2, 3, 5)
GROUP BY c.CityName

Stores count in each city where CityId IN(4, 6, 7, 8):

SELECT c.CityName, COUNT(c.id) AS StoresInCity
FROM Stores s
INNER JOIN Malls m ON s.mallid = m.id
INNER JOIN City c ON m.cityid = c.id
WHERE m.CityId IN (4, 6, 7, 8)
GROUP BY c.CityName

Answer 2

Here's one query which gives you all 3 answers:

SELECT cityId,
       storesPerCity,
       SUM (CASE WHEN cityId IN (1,2,3,5) THEN storesPerCity ELSE 0 END) NumStores1_2_3_5,
       SUM (CASE WHEN cityId IN (4,6,7,8) THEN storesPerCity ELSE 0 END) Other
FROM (
       SELECT c.Id cityId,
              COUNT(*)  storesPerCity         
       FROM Stores s INNER JOIN 
            Malls m ON s.Mallid = m.Id INNER JOIN
            City c ON m.CityId = c.Id
       GROUP BY c.Id) x
GROUP BY cityId, storesPerCity