I have a table which has several one to many relationships with other tables. Let's say the main table is a person, and the other tables represent pets, cars and children. I would like a query that returns details of the person,the number of pets, cars and children they have e.g.
Person.Name Count(cars) Count(children) Count(pets)
John Smith 3 2 4
Bob Brown 1 3 0
What is the best way to do this?
Subquery Factoring (9i+):
WITH count_cars AS (
SELECT t.person_id
COUNT(*) num_cars
FROM CARS c
GROUP BY t.person_id),
count_children AS (
SELECT t.person_id
COUNT(*) num_children
FROM CHILDREN c
GROUP BY t.person_id),
count_pets AS (
SELECT p.person_id
COUNT(*) num_pets
FROM PETS p
GROUP BY p.person_id)
SELECT t.name,
NVL(cars.num_cars, 0) 'Count(cars)',
NVL(children.num_children, 0) 'Count(children)',
NVL(pets.num_pets, 0) 'Count(pets)'
FROM PERSONS t
LEFT JOIN count_cars cars ON cars.person_id = t.person_id
LEFT JOIN count_children children ON children.person_id = t.person_id
LEFT JOIN count_pets pets ON pets.person_id = t.person_id
Using inline views:
SELECT t.name,
NVL(cars.num_cars, 0) 'Count(cars)',
NVL(children.num_children, 0) 'Count(children)',
NVL(pets.num_pets, 0) 'Count(pets)'
FROM PERSONS t
LEFT JOIN (SELECT t.person_id
COUNT(*) num_cars
FROM CARS c
GROUP BY t.person_id) cars ON cars.person_id = t.person_id
LEFT JOIN (SELECT t.person_id
COUNT(*) num_children
FROM CHILDREN c
GROUP BY t.person_id) children ON children.person_id = t.person_id
LEFT JOIN (SELECT p.person_id
COUNT(*) num_pets
FROM PETS p
GROUP BY p.person_id) pets ON pets.person_id = t.person_id
you could use the COUNT(distinct x.id) synthax:
SELECT person.name,
COUNT(DISTINCT car.id) cars,
COUNT(DISTINCT child.id) children,
COUNT(DISTINCT pet.id) pets
FROM person
LEFT JOIN car ON (person.id = car.person_id)
LEFT JOIN child ON (person.id = child.person_id)
LEFT JOIN pet ON (person.id = pet.person_id)
GROUP BY person.name
I would probably do it like this:
SELECT Name, PersonCars.num, PersonChildren.num, PersonPets.num
FROM Person p
LEFT JOIN (
SELECT PersonID, COUNT(*) as num
FROM Person INNER JOIN Cars ON Cars.PersonID = Person.PersonID
GROUP BY Person.PersonID
) PersonCars ON PersonCars.PersonID = p.PersonID
LEFT JOIN (
SELECT PersonID, COUNT(*) as num
FROM Person INNER JOIN Children ON Children.PersonID = Person.PersonID
GROUP BY Person.PersonID
) PersonChildren ON PersonChildren.PersonID = p.PersonID
LEFT JOIN (
SELECT PersonID, COUNT(*) as num
FROM Person INNER JOIN Pets ON Pets.PersonID = Person.PersonID
GROUP BY Person.PersonID
) PersonPets ON PersonPets.PersonID = p.PersonID
Note, that it depends on your flavour of RDBMS, whether it supports nested selects like the following:
SELECT p.name AS name
, (SELECT COUNT(*) FROM pets e WHERE e.owner_id = p.id) AS pet_count
, (SELECT COUNT(*) FROM cars c WHERE c.owner_id = p.id) AS world_pollution_increment_device_count
, (SELECT COUNT(*) FROM child h WHERE h.parent_id = p.id) AS world_population_increment
FROM person p
ORDER BY p.name
IIRC, this works at least with PostgreSQL and MSSQL. Not tested, so your mileage may vary.
Using subselects not very good practice, but may be here it will be good
select p.name, (select count(0) from cars c where c.idperson = p.idperson),
(select count(0) from children ch where ch.idperson = p.idperson),
(select count(0) from pets pt where pt.idperson = p.idperson)
from person p
You could do this with three outer joins:
SELECT
Person.Name,
sum(case when cars.id is not null then 1 else 0 end) car_count,
sum(case when children.id is not null then 1 else 0 end) child_count,
sum(case when pets.id is not null then 1 else 0 end) pet_count
FROM
Person
LEFT OUTER JOIN
cars on
Person.id = cars.person_id
LEFT OUTER JOIN
children on
Person.id = children.person_id
LEFT OUTER JOIN
pets on
Person.id = pets.person_id
GROUP BY
Person.Name
I belive that Oracle now supports the case when syntax, but if not you could use a decode.
You'd need to include multiple count statements in the query. Off the top of my head,
SELECT p.Name, COUNT(DISTINCT t.Cars), COUNT(DISTINCT o.Children), Count(DISTINCT p.Pets)
FROM Person p
INNER JOIN Transport t ON p.ID = t.PersonID
LEFT JOIN Offspring o ON p.ID = o.PersonID
LEFT JOIN Pets p ON p.ID = o.OwnerID
GROUP BY p.Name
ORDER BY p.Name
Related
TABLE student: ID, ID2, NAME, AGE
TABLE class: ID, CLASS_NAME, some other columns
TABLE school: ID2, some other columns.
I am trying to perform below in Oracle SQL:
If the count of the records in TABLE "student" with age>5, is 1,
join the student table with "CLASS" table by "ID", else, join the student table with "school" table by "ID2".
I found I cannot put count in where clause. Can someone help?
I would use window functions:
select s.*, . . .
from (select s.*, sum(case when age > 5 then 1 else 0 end) over () as cnt5
from students s
) s left join
class c
on c.id = s.id and cnt5 = 1 left join
school sch
on sch.id2 = s.id2 and cnt5 <> 1
where c.id is not null or sch.id is not null
you can use left join with case
select s.*, case when age > 5 then COALESCE (c.ID,scl.ID2) as id
from student s
left join class c on s.ID=c.ID
left join school scl on s.ID2=scl.ID2
As Gordon said window functions are an option, but this is also a rare occasion where you can deliberately perform a cross join:
select s.*
,...
from students s
left join
(
select count(*) as RECORD_COUNT
from students
where age > 5
) sub
on 1 = 1
left join class c
on s.id = c.id
and sub.record_count = 1
left join school h
on s.id2 = h.id2
and c.id is null
I have two tables in Oracle DB
Person (
id
)
Bill (
id,
date,
amount,
person_id
)
I need to get person and amount from last bill if exist.
I trying to do it this way
SELECT
p.id,
b.amount
FROM Person p
LEFT JOIN Bill b
ON b.person_id = p.id AND b.date = (SELECT MAX(date) FROM Bill WHERE person_id = 1)
WHERE p.id = 1;
But this query works only with INNER JOIN. In case of LEFT JOIN it throws ORA-01799 a column may not be outer-joined to a subquery
How can I get amoun from the last bill using left join?
Please try the below avoiding sub query to be outer joined
SELECT
p.id,
b.amount
FROM Person p
LEFT JOIN(select * from Bill where date =
(SELECT MAX(date) FROM Bill b1 WHERE person_id = 1)) b ON b.person_id = p.id
WHERE p.id = 1;
What you are looking for is a way to tell in bills, for each person, what is the latest record, and that one is the one to join with. One way is to use row_number:
select * from person p
left join (select b.*,
row_number() over (partition by person_id order by date desc) as seq_num
from bills b) b
on p.id = b.person_id
and seq_num = 1
You cannot have a subquery inside an ON statement.
Instead you need to convert your LEFT JOIN statement into a whole subquery.
Not tested but this should work.
SELECT
p.id,
b.amount
FROM Person p
LEFT JOIN (
SELECT id FROM Bill
WHERE person_id = p.id
AND date = (SELECT date FROM Bill WHERE person_id = 1)) b
WHERE p.id = 1;
I'm not quite sure why you would want to filter for the date though.
Simply filtering for the person_id should do the trick
you should join Person and Bill to the result for max date in bill related to person_id
select Person.id, bill.amount
from Person
left join bill on bill.person_id = person.id
left join (
select person_id, max(date) as max_date
from bill
group by person_id ) t on t.person_id = Person.id and b.date = t.max_date
Hey you can do like this
SELECT
p.id,
b.amount
FROM Person p
LEFT JOIN Bill b
ON b.person_id = p.id AND b.date = (SELECT max(date) FROM Bill WHERE person_id = 1)
WHERE p.id = 1
SELECT
p.id,
b.amount
FROM Person p
LEFT JOIN Bill b
ON b.person_id = p.id
WHERE (SELECT max(date) FROM bill AS sb WHERE sb.person_id=p.id LIMIT 1)=b.date;
SELECT
p.id,
c.amount
FROM Person p
LEFT JOIN (select b.person_id as personid,b.amount as amount from Bill b where b.date1= (select max(date1) from Bill where person_id=1)) c
ON c.personid = p.id
WHERE p.id = 1;
try this
select * from person p
left join (select MAX(id) KEEP (DENSE_RANK FIRST ORDER BY date DESC)
from bills b) b
on p.id = b.person_id
I use GREATEST() function in join condition:
SELECT
p.id,
b.amount
FROM Person p
LEFT JOIN Bill b
ON b.person_id = p.id
AND b.date = GREATEST(b.date)
WHERE p.id = 1
This allows you to grab the whole row if necessary and grab the top x rows
SELECT p.id
,b.amount
FROM person p
LEFT JOIN
(
SELECT * FROM
(
SELECT date
,ROW_NUMBER() OVER (PARTITION BY person_id ORDER BY date DESC) AS row_num
FROM bill
)
WHERE row_num = 1
) b ON p.id = b.person_id
WHERE p.id = 1
;
My below query using two select statements works:
create or replace view q2 as
select count(p.id) nstudents,
(select count(p.id) nstaff
from people p, staff s where p.id = s.id)
from people p, students s where p.id = s.id;
but when i include a third sub query:
create or replace view q2 as
select count(p.id) nstudents,
(select count(p.id) nstaff,
(select count(p.id) nboth
from people p, students s, staff t where p. id = s.id and p.id = t.id)
from people p, staff t where p.id = t.id)
from people p, students s where p.id = s.id;
it gives me the following error:
ERROR: subquery must return only one column
LINE 3: (select count(p.id) nstaff,
Am i making some mistake while including a third query or is there a limit of just 2 nested select statements?
The version with the additional sub-query fails because you insert the second sub-query into the first, when it should come after it like this:
select count(p.id) nstudents,
(select count(p.id) from people p, staff t where p.id = t.id) nstaff ,
(select count(p.id) from people p, students s, staff t where p. id = s.id and p.id = t.id) nboth
from people p, students s where p.id = s.id;
However, the query could just as well be written using conditional aggregation (and to use explicit ANSI standard joins) like this:
select
sum(case when s.id is not null then 1 end) nstudents,
sum(case when t.id is not null then 1 end) nstaff,
sum(case when s.id is not null and t.id is not null then 1 end) nboth
from people p
left join students s on p. id = s.id
left join staff t on p.id = t.id
I have PostgreSQL database and I try to print all my users (Person).
When I execute this query
-- show owners
-- sorted by maximum cars amount
SELECT p.id
FROM car c JOIN person p ON c.person_id = p.id
GROUP BY p.id
ORDER BY COUNT(p.name) ASC;
I get all owners sorted by cars amount
Output: 3 2 4 1
And all order goes wrong when I try to link owner id.
SELECT *
FROM person p
WHERE p.id IN (
SELECT p.id
FROM car c JOIN person p ON c.person_id = p.id
GROUP BY p.id
ORDER BY COUNT(p.name) ASC);
Output: 1 2 3 4 and other data
You see than order is wrong. So here is my question how can I save that order?
Instead Of subquery use join. Try this.
SELECT p.*
FROM person p
JOIN (SELECT p.id,
Count(p.NAME)cnt
FROM car c
JOIN person p
ON c.person_id = p.id
GROUP BY p.id) b
ON p.id = b.id
ORDER BY cnt ASC
Untangle the mess. Aggregate first, join later:
SELECT p.*
FROM person p
JOIN (
SELECT person_id, count(*) AS ct
FROM car
GROUP BY person_id
) c ON c.person_id = p.id
ORDER BY c.cnt;
No need to join to person twice. This should be fastest if you count most or all rows.
For a small selection, correlated subqueries are faster:
SELECT p.*
FROM person p
ORDER BY (SELECT count(*) FROM car c WHERE c.person_id = p.id)
WHERE p.id BETWEEN 10 AND 20; -- some very selective predicate
As for your original: IN takes a set on the right hand, order of elements is ignored, so ORDER BY is pointless in the subuery.
I have the following tables:
Person, {"Id", "Name", "LastName"}
Sports, {"Id" "Name", "Type"}
SportsPerPerson, {"Id", "PersonId", "SportsId"}
For my query I want to get all the Persons that excersise a specific Sport whereas I only have the Sports "Name" attribute at my disposal. To retrieve the correct rows I've figured out the following queries:
SELECT *
FROM Person
WHERE Person.Id in
(
SELECT SportsPerPerson.PersonId FROM SportsPerPerson
INNER JOIN Sports on SportsPerPerson.SportsId = Sports.Id
WHERE Sports.Name = 'Tennis'
)
AND Person.Id in
(
SELECT SportsPerPerson.PersonId FROM SportsPerPerson
INNER JOIN Sports on SportsPerPerson.SportsId = Sports.Id
WHERE Sports.Name = 'Soccer'
)
OR
SELECT *
FROM Person
WHERE Id IN
(SELECT PersonId FROM SportsPerPerson WHERE SportsId IN
(SELECT Id FROM Sports WHERE Name = 'Tennis'))
AND Id IN
(SELECT PersonId FROM SportsPerPerson WHERE SportsId IN
(SELECT Id FROM Sports WHERE Name = 'Soccer'))
Now my question is, isn't there an easier way to write this query? Using just OR won't work because I need the person who play 'Tennis' AND 'Soccer'. But using AND also doesn't work because the values aren't on the same row.
You can use another JOIN to avoid the second IN. The sub-select only returns those persons that play both Tennis and Soccer:
SELECT *
FROM Person
WHERE Person.Id IN
(
SELECT spp1.PersonId
FROM SportsPerPerson spp1
JOIN SportsPerPerson spp2 ON ( spp2.PersonId = spp1.PersonId )
JOIN Sports s1 on spp1.SportsId = s1.Id
JOIN Sports s2 on spp2.SportsId = s2.Id
WHERE s1.Name = 'Tennis'
AND s2.Name = 'Soccer'
)
You should use two joins in the query:
SELECT *
FROM Person p INNER JOIN SportsPerPerson spp1 ON (p.PersonId = spp1.PersonId)
INNER JOIN Sports s1 ON (s1.SportsIN = spp1.SportId)
INNER JOIN SportsPerPerson spp2 ON (p.PersonId = spp2.PersonId)
INNER JOIN Sports s2 ON (s2.SportId = spp2.SportId)
WHERE s1.Name = 'Tennis' AND s2.Name='Soccer'
The trick is to use aliases so that you can use the same tables multiple times:
SELECT p.*
FROM Person p
INNER JOIN SportsPerPerson spa
ON p.Id = spa.PersonId
INNER JOIN Sports sa
ON spa.SportsId = sa.Id
INNER JOIN SportsPerPerson spb
ON p.Id = spb.PersonId
INNER JOIN Sports sb
ON spb.SportsId = sb.Id
WHERE
sa.Name = 'Tennis'
AND sb.Name = 'Soccer'
This:
SELECT *
FROM Person p
WHERE (
SELECT COUNT(*)
FROM Sports s
JOIN SportsPerPerson sp
ON sp.SportsID = s.id
WHERE s.name IN ('Tennis', 'Soccer')
AND sp.PersonID = p.id
) = 2
or this:
SELECT p.*
FROM (
SELECT sp.PersonID
FROM Sports s
JOIN SportsPerPerson sp
ON sp.SportsID = s.id
WHERE s.name IN ('Tennis', 'Soccer')
GROUP BY
sp.PersonID
HAVING COUNT(*) = 2
) q
JOIN person p
ON p.id = q.personID
You need to declare a UNIQUE KEY or a PRIMARY KEY on SportsPerPerson (sportsid, personid) for this to work correctly and fast.
The query you need is:
SELECT p.ID, p.Name, p.LastName
FROM Person p
JOIN SportsPerPerson sp ON p.ID = sp.PersonID
JOIN Sports s ON sp.SportsID = s.ID
WHERE s.Name = 'Football'
That said, as an aside, the ID key on the SportsPerPerson table is entirely unnecessary to implement the many to many relationship you have. Using the PersonID and SportID columns as a composite primary key would be enough.