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.
Related
I am trying to use a Set operator to show country names(Table A col.) without a city(Table B col.) and cities(B) without a country(A). I have also tried to write this query using LEFT JOINS, which I show below and I included Table C(Regions) because I am not sure whether to use that primary key in a LEFT JOIN.
Table A (Countries):
Column_name | Column_id
|
COUNTRY_ID | 1
COUNTRY_NAME | 2
REGION_ID | 3
Table B (Locations):
Column_name | Column_id
|
LOCATION_ID | 1
CITY | 4
COUNTRY_ID | 6
Table C(Regions):
Column_name | Column_id
|
REGION_ID | 1
I have tried the following:
SELECT c.country_name, l.city
FROM Countries c
LEFT JOIN Locations l ON c.country_id = l.country_id
UNION
SELECT c2.country_name, l2.city
FROM Countries c2
LEFT JOIN Locations l2 ON c2.country_id = l2.country_id;
The SQL statement above returned all Table A values, and Table A values that do not contain Table B values (Countries that do not have Cities).
I also tried this statement below and got the exact same result:
SELECT c.country_name, l.city
FROM Countries c
LEFT JOIN Locations l ON c.country_id = l.country_id
LEFT JOIN Regions r ON r.region_id = c.region_id;
The one thing it is missing is Table A values not found in Table B (Countries not found in Cities.)
There are a lot of options to get your desired result. One way is to use LEFT JOIN to get the countries without city and RIGHT JOIN to get the cities without country:
SELECT c.country_name, l.city
FROM countries c
LEFT JOIN locations l ON c.country_id = l.country_id
WHERE l.city IS NULL
UNION ALL
SELECT c.country_name, l.city
FROM countries c
RIGHT JOIN locations l ON c.country_id = l.country_id
WHERE c.country_name IS NULL;
Another possibility is to use two LEFT JOIN, but starting from the opposite table, like this:
SELECT c.country_name, l.city
FROM countries c
LEFT JOIN locations l ON c.country_id = l.country_id
WHERE l.city IS NULL
UNION ALL
SELECT c.country_name, l.city
FROM locations l
LEFT JOIN countries c ON c.country_id = l.country_id
WHERE c.country_name IS NULL;
If you don't like using JOIN at all, you can do this using NOT IN:
SELECT c.country_name, NULL city
FROM countries c
WHERE country_id NOT IN (SELECT country_id FROM locations)
UNION ALL
SELECT NULL country_name, l.city
FROM locations l
WHERE country_id NOT IN (SELECT country_id FROM countries);
Or if you prefer NOT EXISTS, this will work, too:
SELECT c.country_name, NULL city
FROM countries c
WHERE NOT EXISTS (SELECT 1 FROM locations WHERE country_id = c.country_id)
UNION ALL
SELECT NULL country_name, l.city
FROM locations l
WHERE NOT EXISTS (SELECT 1 FROM countries WHERE country_id = l.country_id);
I created an example that shows all these queries will produce the identic outcome: db<>fiddle
Add ORDER BY c.country_name and ORDER BY l.city to the queries in case you want the result set to be sorted by them.
A last, but important note: As you see, I used UNION ALL instead of UNION because I don't see a reason why to use UNION in your use case. UNION ALL is much faster, so I recommend to use that unless there is a really convincing reason to do not use it. The only advantage of UNION is that it does not show duplicate rows, but I think they are very unlikely in your situation, so it should not be required.
The simplest illustration of using a set operator to find countries without cities would be:
select country_id from countries
minus
select country_id from locations
COUNTRY_ID
----------
1
4
As you need the country name, you just need to look it up:
select country_name from countries
minus
select c.country_name from locations l
join countries c on c.country_id = l.country_id;
COUNTRY_NAME
-----------------
England
Italy
Cities without a country (or with an invalid country code) is simpler as a left join and filter:
select l.city, l.country_id
from locations l
left join countries c on c.country_id = l.country_id
where c.country_id is null
CITY
-----------------
Berlin
Tokyo
If the requirement really is to do this using set operators, you would (conceptually) look for cities whose country_id is in the set of (location countries minus city countries):
select l.location_id, l.city, l.country_id
from locations l
where l.country_id in
( select country_id from locations
minus
select country_id from countries )
However this wouldn't give you locations whose country_id was null.
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
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
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