We have two tables Country and CountryStates with the following fields
Country
- CountryId
- CountryName
CountryStates
- StateId
- StateName
- CountryId
There are some Countries without any states added in the database.
Now we have to fetch only those countries where states are added.
You can use this query to retrieve only countries that have a state:
SELECT *
FROM Country AS C
WHERE EXISTS (SELECT TOP 1 1
FROM CountryStates CS
WHERE CS.CountryId = C.CountryId
)
Use Exists like this
SELECT CountryID,CountryName
FROM Country C
WHERE EXISTS
(
SELECT 1
FROM CountryStates S
WHERE S.CountryID = C.CountryID
)
You can perform a JOIN (also known as INNER JOIN) on CountryStates, using the CountryId.
This will leave you with only the details of Countries which have a state added for them.
SELECT *
FROM Country
INNER JOIN CountryStates ON Country.CountryId = CountryStates.CountryId
Same Result can be obtained by using sample INNER JOIN..
SELECT CountryID,CountryName
FROM Country C
INNER JOIN CountryStates S
ON C.CountryID = S.CountryID
Related
I have a Set of tables
Hotels
Countries
Regions
Cities
Hotel_Types
and a many to many relations table named Mappings which contains all the relations/mappings which contains info like
id, hotel_id, reference_type, reference_id, ...
where reference_type can be a Country, Region, City, Hotel_Type etc
and reference_id is the id of said entity like country_id or city_id etc.
I need to create a list of all possible combinations of
Country_Name+Hotel_Type_Name
Region_Name+Hotel_Type_Name
City_Name+Hotel_Type_Name
Where the hotels exist. Any help how may I access the names from different tables and how to combine them
I am implying few things here but you could do inner joins in this way:
select name, hotel_type_name
from (select c.country_name as name, h.hotel_type_name Mappings m inner join Countries c on m.reference_type='Country' and m.reference_id=c.country_id inner join hotel_Types h on m.reference_type='Hotel_type' and m.reference_id=h.hotel_type_id) union all
(select c.region_name as name, h.hotel_type_name Mappings m inner join Regions r on m.reference_type='Region' and m.reference_id=r.region_id inner join Hotel_Types h on m.reference_type='Hotel_type' and m.reference_id=h.hotel_type_id) union all
(select c.city_name as name, h.hotel_type_name Mappings m inner join Cities ci on m.reference_type='City' and m.reference_id=ci.city_id inner join Hotel_Types h on m.reference_type='Hotel_type' and m.reference_id=h.hotel_type_id)
This will list unique combinations of Country_Name+Hotel_Type_Name
--link hotels to hotel_type
with Hotel_Hotel_Types as (
select h.hotel_id
,ht.reference_id as hotel_types_id
from Hotels as h
inner join Mappings ht on ht.reference_type = 'Hotel_Type' and h.hotel_id = ht.hotel_id
)
--link hotels to Country_Name
,Hotel_Country_Name as (
select h.hotel_id
,c.reference_id as countries_id
from Hotels as h
inner join Mappings c on c.reference_type = 'Country' and h.hotel_id = c.hotel_id
)
select distinct ht.*, c.*
from Hotel_Hotel_Types hht
inner join Hotel_Types ht on ht.hotel_types_id = hht.hotel_types_id
inner join Hotel_Country_Name hc on hc.hotel_id = hht.hotel_id
inner join Countries c on с.countries_id = hc.countries_id
Region_Name+Hotel_Type_Name and City_Name+Hotel_Type_Name can be queried using similar sqls.
I have 3 tables: COUNTRY, STATE, CITY
This is my Country table with two columns:
CountryID, Name
This is my State table:
This is my City table:
I want to retrieve the count of states and cities according to the country table using join query.
Skipping the fact that your question is not asked well - try this query, it should work for you:
WITH
tab_a AS (
SELECT c.countryid, COUNT (s.stateid) AS state_num
FROM country c
LEFT JOIN state s ON c.countryid = s.countryid
GROUP BY c.countryid
),
tab_b AS (
SELECT c.countryid, COUNT (cc.cityid) city_num
FROM country c
LEFT JOIN state s ON c.countryid = s.countryid
LEFT JOIN city cc ON s.stateid = cc.stateid
GROUP BY c.countryid
)
SELECT a.countryid,
a.state_num,
b.city_num
FROM tab_a a JOIN tab_b b ON a.countryid=b.countryid
I have a table named Actor, with only a column for City (CityId). I want to return the number of actors in a particular State (StateId). The catch however is that I have separate tables for City, County, and finally State (City has CountyId, County has StateId). How do I this in a T-SQL query?
I have a solution that involves nested Select statements, something like:
SELECT COUNT(1)
FROM Actor a
WHERE a.CityId IN
(SELECT CityId FROM City WHERE CountyId IN...)
...but is there a more efficient way to do this? Thanks
You can use this query to get your output
----------------------------------------------------------
SELECT COUNT(ActorId)
FROM Actor a
INNER JOIN City c ON a.cityId = c.cityId
INNER JOIN Country con ON c.countryId = con.countryId
INNER JOIN STATE s ON con.stateId = s.stateId
GROUP BY s.stateId
Use JOINS to query your data.
I am using INNER JOIN here.
Assuming that you have CountryId in your City Table, You can do it following way.
In case you don't have countryId in your City Table you have to apply one more INNER JOIN on State Table.
SELECT COUNT(1) FROM Actor a INNER JOIN
City b ON a.CityId = b.CityId
WHERE b.CountryId IN (...)
You can easily put the JOINS across different table that you have and then use the Group By clause to find out the total number of actors from specific state.
I have used the column name on the basis of my wild guess, you can change them with the original name that you have in your database.
SELECT StateId,
Count(ActorId) AS Total
FROM ACTOR
INNER JOIN City ON Actor.CityId = City.CityId
INNER JOIN County ON County.CountyId = City.CountyId
INNER JOIN State ON State.StateId = County.StateId
GROUP BY State.StateId
Assuming the relation names, you can do something like this with joins:
select s.ID, s.Name, count(*)
from Actors a
inner join Cities c on c.ID = a.CityID
inner join County cn on cn.ID = c.CountyID
inner join State s on s.ID = cn.StateID
group by s.ID, s.Name
If you only need the StateId you don't even need to join with states, this will do:
select cn.StateID, count(*)
from Actors a
inner join Cities c on c.ID = a.CityID
inner join County cn on cn.ID = c.CountyID
group by cn.StateID
Tables:
Country
-------
PK CountryID
Name
City
-------
PK CityID
FK CountryID
Name
Airport
--------
PK AirportID
FK CityID
Name
My task is to select names of countries that have no airport.
I can imagine only one solution with EXCEPT (or MINUS)
SELECT Country.Name
FROM Country EXCEPT (SELECT DISTINCT Country.Name FROM Country, City, Airport
WHERE City.CountryID = Country.CountryID AND Airport.CityID = City.CityID);
But is it possible not to use EXCEPT but something like IS NULL?
SELECT cn.CountryID
FROM Country cn
LEFT JOIN City ct ON cn.CountryID = ct.CountryID
LEFT JOIN Airport ar on ar.CityID=ct.CityID
WHERE ar.AirportID is null
If you need to make this query with IS NULL try following query:
SQLFiddle demo
select ct.CountryId,max(ct.Name) from Country ct
left join City c on ct.CountryId=c.CountryId
left join Airport a on a.CityId=c.CityID
group by ct.CountryId
HAVING max(a.AirportID) IS NULL
You can use this, but it's basically the same thing you have with different syntax.
SELECT Country.Name
FROM Country
Where Country.Name Not IN
(
SELECT DISTINCT Country.Name FROM Country, City, Airport
WHERE City.CountryID = Country.CountryID AND Airport.CityID = City.CityID
);
I have self join table. This table is being used to join up to 4 level, i.e.;
Region -> Country -> County -> Town
How can I get Parent of Parent of Town. To do this up to two level this is the query
SELECT t.ShortName AS Town,
(SELECT c.ShortName FROM Locations c
WHERE c.LocationId = t.ParentId) AS County
FROM Locations t
WHERE t.LocationId = 100
Now want to get Country which is parent of County.
Either hardcode another join or use a recursive CTE.
;with locs as
(
select 1 as level, ShortName, ParentId
from Locations
WHERE LocationId = 100
UNION ALL
SELECT level + 1, l.ShortName, l.ParentId
FROM Locations l
JOIN locs ON locs.ParentId = l.LocationId
)
SELECT * FROM locs;
Just pretend its 4 separate tables, using nicely named aliases:
SELECT town.ShortName as TownName,
county.ShortName as CountyName,
country.ShortName as CountryName,
region.ShortName as RegionName
FROM Locations town
INNER JOIN Locations county ON town.ParentID = county.LocationID
INNER JOIN Locations country ON county.ParentID = country.LocationID
INNER JOIN Locations region ON country.ParentID = region.LocationID
WHERE town.LocationID = 100
If not every town has a county, country, and region, then some of those might need to be LEFT OUTER joins.