I have two tables
Cities:
id name
------------
1 Helsinki
2 Tukholma
3 Oslo
4 Turku
Flights
id where_id to_id
---------------------
1 1 2
2 1 3
3 2 3
4 2 4
I want to get this result
Helsinki Tukholma
Helsinki Oslo
Tukholma Oslo
Tukholma Turku
How do I compose the query? Result has two name columns and I can't get around it?
You can join twice:
select c1.name where_city, c2.name to_city
from flights f
inner join cities c1 on c1.id = f.where_id
inner join cities c2 on c2.id = f.to_id
You need two joins:
select f.*, cw.name, ct.name
from flights f join
cities cw
on f.where_id = cw.id join
cities ct
on f.to_id = ct.id;
I found this solution. Pretty clear. No JOINs
SELECT A.name, B.name FROM cities A, cities B, flights F WHERE F.where_id=A.id AND L.to_id=B.id;
Related
I'm doing an inner join on a table like this:
SELECT *
FROM patient p
INNER JOIN
vaccine v
ON
p.vaccine_id = v.id
The condition f.vac_1 = mv.id might not been satisfied in the case where a person have not been vaccinated. In such case, I don't want to ignore the row, but instead of displaying the vaccine name (which is the purpose of the inner join) to display an emtpy string.
How can this be done ?
Example
Table vaccinne
id
name
1
Moderna
2
Comirnaty
3
Janssen
Table patient
id
name
vaccine_id
1
john
1
2
kermit
2
3
jessica
I'm looking for a query to produce:
id
name
vaccine_id
1
john
Moderna
2
kermit
Comirnaty
3
jessica
If I understand correctly, you want a left join starting with foo:
SELECT *
FROM foo f LEFT JOIN
vac v
ON f.vac_1 = mv.id
I want to run an sql query and find all the books that have type="adventure" AND type="drama".
AND does not allow searching at the same time 2 different values of the same column.
My tables are like this
Books
Bid Bname Author
1 Sql loren
2 Monster Mike
3 Minnie Michel
----------
Copies
Cid Bid Type
1 1 Science
2 1 Teaching
3 2 Adventure
4 3 Romance
5 3 Drama
6 3 Adventure
The result I want:
Bid Title
3 Minnie
The tables can't change
There are several ways to do it, here is one using two exists conditions. Bottom line is that you have to check copies table twice.
SELECT * FROM books b
WHERE EXISTS
(
SELECT * FROM copies c1
WHERE b.bid = c1.bid
AND c1.type='adventure'
)
AND EXISTS
(
SELECT * FROM copies c2
WHERE b.bid = c2.bid
AND c2.type='drama'
)
You can achieve with JOIN, here is the DEMO. And you can use EXISTS as per #NenadZivkovic answer.
select
b.Bid,
Bname as Title
from books b
join Copies c
on b.Bid = c.Bid
and c.Type ='Drama'
join Copies c1
on c.Bid = c1.Bid
and c1.Type = 'Adventure'
group by
b.Bid,
Bname
order by
b.Bid
Master table
SerNo HospitalId CityId
1 1 1
2 1 1
3 2 2
4 3 2
5 1 1
HospitalMaster
HospitalId HospitalName
1 ABC
2 XYZ
CityMaster
CityId City
1 Delhi
2 Bombay
Result
I need something like this
City TotalHospital
Delhi 1
Bombay 2
I tried joining the tables but I keep getting the total rows of the columns and not of the hospitals.
Thank you.
Left join the city master table to a subquery which finds the hospital counts for each city. Note carefully that we only count distinct hospitals, because a hospital city relationship may appear more than once in the master table.
SELECT t1.City, COALESCE(t2.cnt, 0) AS TotalHospital
FROM CityMaster t1
LEFT JOIN
(
SELECT CityId, COUNT(DISTINCT HospitalId) cnt
FROM Master
GROUP BY CityID
) t2
ON t1.CityId = t2.CityId;
Demo
Try this:
SELECT C.City,COUNT(DISTINCT HospitalID)TotalHospital
FROM CityMaster C
JOIN Master_table M ON M.CityId=C.CityId
GROUP BY C.City
You could apply join
select M.City,count(distinct M.HospitalId) from CityMaster C inner join Master M ON C.CityId = M.CityId
group by M.City
You can do it with using JOIN
Just replace #city, #hospital, #table with your table names.
select C.City,T.CityId from #city C,#hosp H,#table T WHERE T.CityId = C.CityId AND T.HospitalId = H.HospitalId Group by C.City,T.CityId
As we need city name along with count, we can get by join city master and master tables.
select max(C.cityname), count(distinct M.HospitalId)
from CityMaster C
inner join Master M
on C.Cityid = M.CityId
group by M.cityid
OK, I'm an absolute beginner in SQL and I got one task to solve and I'm stuck, so I need help on your ideas how to get the required results.
I have 2 tables - first one is PARENTS, with the following data:
ID Name Age
1 John 25
2 Peter 28
3 Anny 30
4 Jack 32
and the second table is CHILDRENS, with the following data:
children_id parent_id name age
1 1 mary 5
2 1 Susanne 4
3 2 stephen 12
4 4 Kevin 7
What SQL command can be used to get following result:
id parent name number of childrens
1 John 2
2 Peter 1
3 Anny 0
4 Jack 1
Thanks in advance!
Try like this
select PARENTS.id,PARENTS.name,count(CHILDRENS.name)
from PARENTS left join CHILDRENS on PARENTS.id=CHILDRENS.parent_id
group by PARENTS.id,PARENTS.name
As mentioned by Jarlh in comments, Use LEFT OUTER JOIN + Group by
SELECT p.id,
p.name,
Count(parent_id) as number_of_childrens
FROM PARENTS p
LEFT OUTER JOIN CHILDRENS c
ON c.parent_id = p.ID
Group by p.id,
p.name
select p.id, p.name, count(p.id) as number_of_childrens
from parents p
left join childrens c
on p.parent_id = c.parent_id
group by p.id, p.name
SELECT A.ID
, A.name AS parent_name
, COUNT(B.children_id) AS number_of_children
FROM PARENTS AS A
LEFT JOIN CHILDRENS AS B
ON A.ID = B.parent_id
GROUP BY A.ID
, A.name
A left join, count and group by.
Let's say I have two tables. A students table and an observations table. If the students table looks like:
Id Student Grade
1 Alex 3
2 Barney 3
3 Cara 4
4 Diana 4
And the observations table looks like:
Id Student_Id Observation_Type
1 1 A
2 1 B
3 3 A
4 2 A
5 4 B
6 3 A
7 2 B
8 4 B
9 1 A
Basically, the result I'd like from the query would be the following:
Student Grade Observation_A_Count
Alex 3 2
Barney 3 1
Cara 4 2
Diana 4 0
In other words, I'd like to gather data for each student from the students table and for each student count the number of A observations from the observations table and tack that onto the other information. How do I go about doing this?
This is a simple join and aggregate:
select
a.Student,
a.Grade,
count(b.Id) as Observation_A_Count
from
Student a left join
Observations b on a.Id = b.Student_Id
group by
a.Student,
a.Grade
order by
1
Or, you can use a correlated subquery:
select
a.Student,
a.Grade,
(select count(*) from observations x where x.Student_Id = a.Id) as Observation_A_Count
from
Student a
order by
a.Student
You can join the table with a specific condition, by doing this you can have a field for Observation_B_Count and Observation_C_Count, etc.
SELECT Student.Student, Student.Grade, COUNT(Observation_Type.*) AS Observation_A_Count
FROM Student
LEFT JOIN Observations ON Observations.Student_ID = Student.Student_ID AND Observations.Observation_Type = 'A'
GROUP BY Student.Student, Student.Grade