Database structure:
Clubs: ID, ClubName
Teams: ID, TeamName, ClubID
Players: ID, Name
Registrations: PlayerID, TeamID, Start_date, End_date, SeasonID
Clubs own several teams. Players may get registered into several teams (inside same club or into different club) during one year.
I have to generate a query to list all players that have been registered into DIFFERENT CLUBS during one season. So if player swapped teams that were owned by the same club then it doesn't count.
My attempts so far:
SELECT
c.short_name,
p.surname,
r.start_date,
r.end_date,
(select count(r2.id) from ejl_registration as r2
where r2.player_id=r.player_id and r2.season=r.season) as counter
FROM
ejl_registration AS r
left Join ejl_players AS p ON p.id = r.player_id
left Join ejl_teams AS t ON r.team_id = t.id
left Join ejl_clubs AS c ON t.club_id = c.id
WHERE
r.season = '2008'
having counter >1
I can't figure out how to count and show only different clubs... (It's getting too late for clear thinking). I use MySQL.
Report should be like: Player name, Club name, Start_date, End_date
This is a second try at this answer, simplifying it to merely count the distinct clubs, not report a list of club names.
SELECT p.surname, r.start_date, r.end_date, COUNT(DISTINCT c.id) AS counter
FROM ejl_players p
JOIN ejl_registration r ON (r.player_id = p.id)
JOIN ejl_teams t ON (r.team_id = t.id)
JOIN ejl_clubs c ON (t.club_id = c.id)
WHERE r.season = '2008'
GROUP BY p.id
HAVING counter > 1;
Note that since you're using MySQL, you can be pretty flexible with respect to columns in the select-list not matching columns in the GROUP BY clause. Other brands of RDBMS are more strict about the Single-Value Rule.
There's no reason to use a LEFT JOIN as in your example.
Okay, here's the first version of the query:
You have a chain of relationships like the following:
club1 <-- team1 <-- reg1 --> player <-- reg2 --> team2 --> club2
Such that club1 must not be the same as club2.
SELECT p.surname,
CONCAT_WS(',', GROUP_CONCAT(DISTINCT t1.team_name),
GROUP_CONCAT(DISTINCT t2.team_name)) AS teams,
CONCAT_WS(',', GROUP_CONCAT(DISTINCT c1.short_name),
GROUP_CONCAT(DISTINCT c2.short_name)) AS clubs
FROM ejl_players p
-- Find a club where this player is registered
JOIN ejl_registration r1 ON (r1.player_id = p.id)
JOIN ejl_teams t1 ON (r1.team_id = t1.id)
JOIN ejl_clubs c1 ON (t1.club_id = c1.id)
-- Now find another club where this player is registered in the same season
JOIN ejl_registration r2 ON (r2.player_id = p.id AND r1.season = r2.season)
JOIN ejl_teams t2 ON (r2.team_id = t2.id)
JOIN ejl_clubs c2 ON (t2.club_id = c2.id)
-- But the two clubs must not be the same (use < to prevent duplicates)
WHERE c1.id < c2.id
GROUP BY p.id;
Here's a list of players for one season.
SELECT sub.PlayerId
FROM
(
SELECT
r.PlayerId,
(SELECT t.ClubID FROM Teams t WHERE r.TeamID = t.ID) as ClubID
FROM Registrations r
WHERE r.Season = '2008'
) as sub
GROUP BY PlayerId
HAVING COUNT(DISTINCT sub.ClubID) > 1
Here's a list of players and seasons, for all seasons.
SELECT PlayerId, Season
FROM
(
SELECT
r.PlayerId,
r.Season,
(SELECT t.ClubID FROM Teams t WHERE r.TeamID = t.ID) as ClubID
FROM Registrations r
) as sub
GROUP BY PlayerId, Season
HAVING COUNT(DISTINCT sub.ClubID) > 1
By the way, this works in MS SQL.
SELECT p.Name, x.PlayerID, x.SeasonID
FROM (SELECT DISTINCT r.PlayerID, r.SeasonID, t.ClubID
FROM Registrations r
JOIN Teams t ON t.ID = r.TeamID) x
JOIN Players p ON p.ID = x.PlayerID
GROUP BY p.rName, x.PlayerID, x.SeasonID
HAVING COUNT(*) > 1
Related
I have difficulties joining the tables below for the desired query as stated.
Theatre (Theatre#, Name, Address, MainTel);
Production (P#, Title, ProductionDirector, PlayAuthor);
Performance (Per#, P#, Theatre#, pDate, pHour, pMinute, Comments);
Client (Client#, Title, Name, Street, Town, County, telNo, e-mail);
Ticket Purchase (Purchase#, Client#, Per#, PaymentMethod, DeliveryMethod, TotalAmount)
Required Query
The theater name (for each theater) and the names of clients who have the highest spending in that theater
SELECT T.NAME, C.NAME, SUM(TOTALAMOUNT)
FROM TICKETPURCHASE TP,
THEATRE T,
CLIENT C,
PERFORMANCE PER
WHERE TOTALAMOUNT = (SELECT MAX (TOTALAMOUNT)
FROM TICKETPURCHASE TP2,
THEATRE T2,
PERFORMANCE PER2,
CLIENT C2,
PRODUCTION P2
WHERE T2.NAME = T.NAME
AND T2.THEATRE# = PER2.THEATRE#
AND TP2.CLIENT# = C2.CLIENT#
AND TP2.PER# =PER2.PER#
AND PER2.P# = P2.P# )
AND C.CLIENT# = TP.CLIENT#
AND T.THEATRE# = PER.THEATRE#
AND TP.PER# = PER.PER#
AND PER.P# = P.P#
GROUP BY T.NAME, C.NAME, TOTALAMOUNT
From Oracle 12, you can do it all in a single query if you aggregate by the primary keys for the theatre and the client to get the total spent and then rank the spending in the ORDER BY clause and use the row limiting clause to get the first ranked values:
SELECT MAX(T.NAME) AS theatre_name,
MAX(C.NAME) AS client_name,
SUM(TP.TOTALAMOUNT) AS amount_spent
FROM TICKETPURCHASE TP
INNER JOIN PERFORMANCE PER
ON (TP.PER# = PER.PER#)
INNER JOIN THEATRE T
ON (T.THEATRE# = PER.THEATRE#)
INNER JOIN CLIENT C
ON (C.CLIENT# = TP.CLIENT#)
GROUP BY
T.THEATRE#,
C.CLIENT#
ORDER BY
DENSE_RANK() OVER (
PARTITION BY T.THEATRE#
ORDER BY SUM(TP.TOTALAMOUNT) DESC
)
FETCH FIRST ROW WITH TIES;
In earlier versions, you can use the same technique and filter in an outer query:
SELECT theatre_name,
client_name,
amount_spent
FROM (
SELECT MAX(T.NAME) AS theatre_name,
MAX(C.NAME) AS client_name,
SUM(TP.TOTALAMOUNT) AS amount_spent,
DENSE_RANK() OVER (
PARTITION BY T.THEATRE#
ORDER BY SUM(TP.TOTALAMOUNT) DESC
) As rnk
FROM TICKETPURCHASE TP
INNER JOIN PERFORMANCE PER
ON (TP.PER# = PER.PER#)
INNER JOIN THEATRE T
ON (T.THEATRE# = PER.THEATRE#)
INNER JOIN CLIENT C
ON (C.CLIENT# = TP.CLIENT#)
GROUP BY
T.THEATRE#,
C.CLIENT#
)
WHERE rnk = 1;
I have the following query. This query allows me to produce a list of children and their familymember contacts (contactpupilID).
select s.studentnr,pc.pupilid, pc.contactpupilid, p2.mainmail
from student s
join pupil p on p.id = s.pupilid
join pupilcontact pc on pc.pupilid = p.id
join pupil p2 on p2.id = pc.contactpupilid
where CURRENT_DATE between pc.validfrom and pc.validuntil
order by pc.pupilid
Each child can have 0 to 3 familycontacts (0 because no contact has been added during registration).
Each familycontact (contactpupilid) has an email field. However there are cases where all familycontacts have an email or 1 of them or none of them.
My list needs to select a child with a familycontact(contactpupilid) that has an email. The familycontact that is selected should be the one that has an email.
If none of the familycontacts have an email then it should select the 1st familycontact by default.
This is how it needs to look like
How would I complete this task?
I don't know what you mean by "first record" because SQL tables are unordered. I can assume you mean the one with the smallest contactpupilid.
What you have described is what distinct on does:
select distinct on (s.studentnr) s.studentnr, pc.pupilid, pc.contactpupilid, p2.mainmail
from student s join
pupil p
on p.id = s.pupilid join
pupilcontact pc
on pc.pupilid = p.id join
pupil p2
on p2.id = pc.contactpupilid
where CURRENT_DATE between pc.validfrom and pc.validuntil
order by s.studentnr, (p2.mainmail is not null) desc;
Use ROW_NUMBER() window function in your query to rank the rows that contain an email first:
with cte as (
select s.studentnr, pc.pupilid, pc.contactpupilid, p2.mainmail,
row_number() over (partition by s.studentnr order by p2.mainmail is not null desc, pc.contactpupilid) rn
from student s
join pupil p on p.id = s.pupilid
join pupilcontact pc on pc.pupilid = p.id
join pupil p2 on p2.id = pc.contactpupilid
where CURRENT_DATE between pc.validfrom and pc.validuntil
)
select studentnr, pupilid, contactpupilid, mainmail
from cte
where rn = 1
order by pupilid;
You can do it with CTE like this
with temp as (
select s.studentnr,pc.pupilid, pc.contactpupilid, p2.mainmail,row_number() over (partition by pupilid order by pupilid) as row_number
from student s
join pupil p on p.id = s.pupilid
join pupilcontact pc on pc.pupilid = p.id
join pupil p2 on p2.id = pc.contactpupilid
where CURRENT_DATE between pc.validfrom and pc.validuntil
order by pc.pupilid
)
select *
from temp
where row_number = 1
I have a query that needs to count the field Points. Then returns the highest value. This query does that fine however I now want to link another table 'Team(PlayerID) with Player(PlayerID), So it shows the player team details etc. I attempted to do that normally on how you would join table but keep getting errors. I also do not want to use the order by desc - First row only. (Oracle)
Query:
SELECT PlayerID, COUNT(Points)
SELECT t.*, p.* FROM
team t INNER JOIN
(SELECT PlayerID, COUNT(Points)
FROM Player
WHERE Points = 1
group by PlayerID
HAVING COUNT(Points) = (SELECT MAX(count(Points))
from Player
WHERE Points = 1
group by PlayerID)
) p
ON t.PlayerID = p.PlayerID
....
HAVING COUNT(Points) = (SELECT MAX(sub.cp)
from (SELECT count(Points) as cp
from Player
WHERE Points = 1
group by PlayerID) sub
)
SELECT A.PlayerID, a.TotalPoints, b.[stuff]
FROM (SELECT PlayerID, COUNT(Points)
FROM Player
WHERE Points = 1
group by PlayerID
HAVING COUNT(Points) = (SELECT MAX(count(Points))
from Player
WHERE Points = 1
group by PlayerID)) a
join TEAM b on b.playerid = a.playerid;
There are three tables:
A table about students: s41071030(sno, sname, ssex, sage, sdept)
A table about course: c41071030(cno, cname, cpno, credit)
A table about selecting courses: sc41071030(sno, cno, grade)
Now, I want select the details about a student whose sdept='CS' and he or she has selected the most courses in department 'CS'.
As with any modestly complex SQL statement, it is best to do 'TDQD' — Test Driven Query Design. Start off with simple parts of the question and build them into a more complex answer.
To find out how many courses each student in the CS department is taking, we write:
SELECT S.Sno, COUNT(*) NumCourses
FROM s41071030 S
JOIN sc41071030 SC ON S.Sno = SC.Sno
WHERE S.Sdept = 'CS'
GROUP BY S.Sno;
We now need to find the largest value of NumCourses:
SELECT MAX(NumCourses) MaxCourses
FROM (SELECT S.Sno, COUNT(*) NumCourses
FROM s41071030 S
JOIN sc41071030 SC ON S.Sno = SC.Sno
WHERE S.Sdept = 'CS'
GROUP BY S.Sno
)
Now we need to join that result with the sub-query, so it is time for a CTE (Common Table Expression):
WITH N AS
(SELECT S.Sno, COUNT(*) NumCourses
FROM s41071030 S
JOIN sc41071030 SC ON S.Sno = SC.Sno
WHERE S.Sdept = 'CS'
GROUP BY S.Sno
)
SELECT N.Sno
FROM N
JOIN (SELECT MAX(NumCourses) MaxCourses FROM N) M
ON M.MaxCourses = N.NumCourses;
And we need to get the student details, so we join that with the student table:
WITH N AS
(SELECT S.Sno, COUNT(*) NumCourses
FROM s41071030 S
JOIN sc41071030 SC ON S.Sno = SC.Sno
WHERE S.Sdept = 'CS'
GROUP BY S.Sno
)
SELECT S.*
FROM s41071030 S
JOIN N ON N.Sno = S.Sno
JOIN (SELECT MAX(NumCourses) MaxCourses FROM N) M
ON M.MaxCourses = N.NumCourses;
Lightly tested SQL: you were warned. To test, run the component queries, making sure you get reasonable results each time. Don't move on to the next query until the previous one is working correctly.
Note that the courses table turns out to be immaterial to the query you are solving.
Also note that this may return several rows if it turns out there are several students all taking the same number of courses and that number is the largest number that any student is taking. (So, if there are 3 students taking 7 courses each, and no student taking more than 7 courses, then you will see 3 rows in the result set.)
Aggregate sc41071030 rows to get the counts.
Join the results to s41071030 to:
filter rows on sdept;
get student details;
RANK() the joined rows on the count values.
Select rows with the ranking of 1.
WITH
aggregated AS (
SELECT
sno,
COUNT(*) AS coursecount
FROM
sc41071030
GROUP BY
sno
),
ranked AS (
SELECT
s.*,
RANK() OVER (ORDER BY agg.coursecount DESC) AS rnk
FROM
s41071030 s
INNER JOIN aggregated agg ON s.sno = agg.sno
WHERE
s.sdept = 'CS'
)
SELECT
sno,
sname,
ssex,
sage,
sdept
FROM
ranked
WHERE
rnk = 1
;
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