there is a table in SQL database, called Players:
Players (ID, name, age, gender, score)
where ID is the primary key.
Now I want to write a query to find the following results:
For each age, find the name and age of the player(s) with the highest score among all players of this age.
I wrote the following query:
SELECT P.name, P.age
FROM Players P
WHERE P.score = (SELECT MAX(P2.score) FROM Players P2)
GROUP BY P.age, P.name
ORDER BY S.age
However, the result of the above query is a list of players with the highest score among ALL players across all ages, not for EACH age.
Then I changed my query to the following:
SELECT P.name, P.age, MAX(P.score)
FROM Players P
GROUP BY P.age, P.name
ORDER BY P.age
However, the second query I wrote gives a list of players with each age, but for each age, there are not only the players with the highest score, but also other players with lower scores within this age group.
How should I fix my logic/query code?
Thank you!
You can use rank to do this.
select name, age
from (
SELECT *,
rank() over(partition by age order by score desc) rnk
FROM Players) t
where rnk = 1
Your original query is quite close. You just need to change the subquery to be a correlated subquery and remove the GROUP BY clause:
SELECT P.name, P.age
FROM Players P
WHERE P.score = (SELECT MAX(P2.score) FROM Players P2 WHERE p2.age = p.age)
ORDER BY P.age;
The analytic ranking functions are another very viable method for processing this question. Both methods can take advantage of an index on Players(age, score). This also wants an index on Players(score). With that index, this should have better performance on large data sets.
You can try it also.
SELECT p.name, p.age, p.score
FROM players p
INNER JOIN
(SELECT `age`, MAX(`score`) AS Maxscore
FROM players
GROUP BY `age`) pp
ON p.`age` = pp.`age`
AND p.`score` = pp.Maxscore;
Try it this will resolve your issue :
select p1.name,p1.age,p1.score from players p1 where p1.score =
(SELECT max(score) from players where age = p1.age) group by p1.age;
If you will required all records having same maximum score :
Then you will use this. I have tested both the query on my localhost.
SELECT p1.name,p1.age,p1.score FROM players p1
WHERE p1.score IN (SELECT MAX(score) FROM players GROUP BY age)
Related
Question: Show the names of all players who have the following:
the difference between the minimum and maximum number of games
this players is greater than 5.
select p.name
from player p
join competition c
on c.playerID = p.playerID
where (
(select count(*) from competition
where count(games) > 1
group by playerID
) - (
select count(*) from competition
where count(games) <= 1
group by playerID
))> 5;
I'm kind of lost. I'm not so sure is this the right way, how I should proceed: should I use count and find the minimum and maximum number of games and compare with greater than 5 or should I use instead of count, min and max functions. Would be very grateful, if someone can explain me the logic of this.
Tables:
player competition
------- --------
playerID playerID
name games
birthday date
address
telefon
SELECT
P.Name,
MIN(C.Games) MinGame,
MAX(C.Games) MaxGame,
FROM Player P
INNER JOIN Competition C
ON C.PlayerId = P.PlayerId
GROUP BY P.Id, P.Name
HAVING MAX(C.Games) - MIN(C.Games) > 5
It should be a simple query:
With tab1 AS (Select player.name, min(games) mx_game, max(games) min_game,
max(games) - min(games) diff
from player JOIN competition ON player.player_id = competition.id
group by player.player_id, player.name)
Select tab1.name from tab1
WHERE diff >5;
I am adding player_id in the group by as player_name could be similar for 2 person.
I have to say who is the scientist who have been the most in mission. I tried this code but it wasn't successful:
select name
from scientist, mission
where mission.nums = chercheur.nums
having count(*) = (select max(count(numis)) from mission, scientist where
mission.nums = chercheur.nums
group by name)
I have done several modifications for this request but I only obtain errors (ora-0095 and ora-0096 if I remember correctly).
Also, I create my tables with:
CREATE TABLE Scientist
(NUMS NUMBER(8),
NAME VARCHAR2 (15),
CONSTRAINT CP_CHER PRIMARY KEY (NUMS));
CREATE TABLE MISSION
(NUMIS NUMBER(8),
Country VARCHAR2 (15),
NUMS NUMBER(8),
CONSTRAINT CP_MIS PRIMARY KEY (NUMIS),
CONSTRAINT CE_MIS FOREIGN KEY (NUMS) REFERENCES SCIENTIST (NUMC));
You could count the missions each scientist participated in, and wrap that query in a query with a window function that will rank them according to their participation:
SELECT name
FROM (SELECT name, RANK() OVER (PARTITION BY name ORDER BY cnt DESC) AS rk
FROM (SELECT name, COUNT(*) AS cnt
FROM scientist s
JOIN mission m ON s.nums = m.nums
GROUP BY name) t
) q
WHERE rk = 1
Step 0 : Format your code :-) It would make it much easier to visualize
Step 1 : Get the count of Numis by Nums in the Mission table. This will tell you how many missions were done by each Nums
This is done in the cte block cnt_by_nums
Next to get the name of the scientist by joining cnt_by_nums with scientist table.
After that you want to get only those scientists who have the cnt_by_missions as the max available value from cnt_by_num
with cnt_by_nums
as (select Nums,count(Numis) as cnt_missions
from mission
group by Nums
)
select a.Nums,max(b.Name) as name
from cnt_by_nums a
join scientist b
on a.Nums=b.Nums
group by a.Nums
having count(a.cnt_missions)=(select max(a1.cnt_missions) from cnt_by_nums a1)
I'd write a query like this:
SELECT NAME, COUNTER
FROM
(SELECT NAME, COUNT(*) AS COUNTER
FROM SCIENTIST S
LEFT JOIN MISSION M
ON S.NUMS=M.NUMS
GROUP BY NAME) NUM
INNER JOIN
(SELECT MAX(COUNTER) AS MAX_COUNTER FROM
(SELECT NAME, COUNT(*) AS COUNTER
FROM SCIENTIST S
LEFT JOIN MISSION M
ON S.NUMS=M.NUMS
GROUP BY NAME) C) MAX
ON NUM.COUNTER=MAX.MAX_COUNTER;
(it works on MYSQL, I hope it's the same in Oracle)
As you don't select the name of your scientist (only count their missions) you don't need to join those tables within the subquery. Grouping over the foreign key would be sufficient:
select count(numis) from mission group by nums
You column names are a bit weird but that's your choice ;-)
Selecting only the scientist with the most mission references could be achieved in two ways. One way would be your approach where you may get multiple scientists if they have the same max missions.
The first problem you have in your query is that you are checking an aggregation (HAVING COUNT(*) = ) without grouping. You are only grouping your subselect.
Second, you could not aggregate an aggregation (MAX(COUNT)) but you may select only the first row of that subselect ordered by it's size or select the max of it by subquerying the subquery.
Approach with only one line:
select s.name from scientist s, mission m
where m.nums = s.nums
group by name
having count(*) =
(select count(numis) from mission
group by nums
order by 1 desc
fetch first 1 row only)
Approach with double subquery:
select s.name from scientist s, mission m
where m.nums = s.nums
group by name having count(*) =
(select max(numis) from
(select count(numis) numis from mission group by nums)
)
Second approach would be doing the FETCH FIRST on yur final result but this would give you exactly 1 scientist even if there are multiple with the same max missions:
select s.name from scientist s, mission m
where m.nums = s.nums
group by name
order by count(*) desc
fetch first 1 row only
Doing a cartisian product is not state of the art but the optimizer would make it a "good join" with the given reference in the where clause.
Made these with IBM Db2 but should also work on Oracle.
If you want one row, then in Oracle 12+, you can do:
SELECT name, COUNT(*) AS cnt
FROM scientist s JOIN
mission m
ON s.nums = m.nums
GROUP BY name
ORDER BY COUNT(*) DESC
FETCH FIRST 1 ROW ONLY;
In earlier versions, you would generally use a subquery:
SELECT s.*
FROM (SELECT name, COUNT(*) AS cnt
FROM scientist s JOIN
mission m
ON s.nums = m.nums
GROUP BY name
ORDER BY COUNT(*) DESC
) sm
WHERE rownum = 1;
If you want ties, then generally window functions would be a simple solution:
SELECT s.*
FROM (SELECT name, COUNT(*) AS cnt,
RANK() OVER (ORDER BY COUNT(*) DESC) as seqnum
FROM scientist s JOIN
mission m
ON s.nums = m.nums
GROUP BY name
ORDER BY COUNT(*) DESC
) sm
WHERE seqnum = 1;
I'm trying to write a query that return the name of the Hobby with the minimal average of ages of the persons with that hobby.
I can get the minimal average of the ages hobby, but i cant get the Name attribute of the hobby himself.
This is how I'm getting the minimal age:
SELECT MIN(avg)
FROM (
SELECT AVG(age) as avg
FROM Hobby H NATURAL JOIN Person P NATURAL JOIN Hobbies R
GROUP BY (R.hnum))
The tables are :
Hobby (hnum, hname)
Person (pid, pname, age)
Hobbies (pid, hnum, frequency)
usually i would want to make this block an inner block and then compare between each hobby the min age but because hobby has no min age attribute i cant do it in this way.
I've updated a bit what Ersin Gülbahar suggested to this:
SELECT MIN(avg), name
FROM (
SELECT AVG(age) as avg, min(hname) name
FROM Hobby H NATURAL JOIN Person P NATURAL JOIN Hobbies R
GROUP BY (R.hnum))
But the only problem is that if there are two hobbies with the same minimal avg age this query return only one row.
Any suggestion ?
Try this
SELECT MIN(avg), min(name)
FROM (
SELECT AVG(age) as avg, min(hname) name
FROM Hobby H NATURAL JOIN Person P NATURAL JOIN Hobbies R
GROUP BY (R.hnum))
You can also use TOP 1 and an ORDER BY:
SELECT TOP 1 (R.hnum), (R.hname), AVG(age)
FROM Hobby H NATURAL JOIN Person P NATURAL JOIN Hobbies R
GROUP BY (R.hnum), (R.hname)
ORDER BY AVG(age)
I need to write bunch of queries with a database with the following tables:
Match(homeId, awayId, homeScore, awayScore, date)
League(leagueId, leagueName)
Player(playerId, teamId, playerName, age, position, marketValue, position)
Team(teamId, teamName, leagueId, city)
However, I could not figure out how to write a sql query for the queries like following:
"Find the latest date when Lazio beat Milan in Milan’s home ground."
or
"Find the names of the leagues in which at least one team has at least three
Goalkeepers."
How can I join the Team table with Match table that will give me the matches with team names included. (i.e. homeId, awayId, homeName, awayName) and write these two queries.
Thanks.
For your first requirement, you can use something like this.
select date
from match
where homeid =(select teamid from team where teamname = 'Milan')
and awayId = (select teamid from team where teamname = 'Lazio')
and homeScore < awayScore
For second, use something like below.
select l.leagueName
from league l
inner join Team t
on l.leagueid=t.leagueid
where t.teamid in (
select distinct(teamid) as teamid from player p
where p.position like 'Goalkeeper'
group by teamid
having count(*) >= 3)
Disclaimer: I'm an SQL newb and this is for a class, but I could really use a poke in the right direction.
I've got these three tables:
student(_sid_, sname, sex, age, year, gpa)
section(_dname_, _cno_, _sectno_, pname)
enroll(_sid_, grade, _dname_, _cno_, _sectno_)
(primary keys denoted by underscores)
I'm trying to write an Oracle-compatible SQL query that returns a table with the student's name (student.sname) that has the highest gpa in each section (that's including section.cno and section.sectno) as well as all the other attributes from section.
I've managed to use an aggregate query and GROUP BY to get the maximum GPA for each section:
SELECT MAX(s.gpa), e.cno, e.sectno
FROM enroll e,
student s
WHERE s.sid = e.sid
GROUP BY e.cno, e.sectno
Let alone the other section attributes, I can't even figure out how to tack on the student name (student.sname). If I add it to the SELECT clause, it has to be included in GROUP BY which messes up the rest of the query. If I use this entire query inside the WHERE or FROM clause of an outer query, I can only access the three fields in the table, which isn't that much use.
I know you can't give me the exact answer, but any hints would be appreciated!
Assuming Oracle 9i+, to get only one of the students with the highest GPA (in the event of ties) use:
WITH summary AS (
SELECT e.*,
s.name,
ROW_NUMBER() OVER(PARTITION BY e.cno, e.sectno
ORDER BY s.gpa DESC) AS rank
FROM ENROLL e
JOIN STUDENT s ON s.sid = e.sid)
SELECT s.*
FROM summary s
WHERE s.rank = 1
Non CTE equivalent:
SELECT s.*
FROM (SELECT e.*,
s.name,
ROW_NUMBER() OVER(PARTITION BY e.cno, e.sectno
ORDER BY s.gpa DESC) AS rank
FROM ENROLL e
JOIN STUDENT s ON s.sid = e.sid) s
WHERE s.rank = 1
If you want to see all students who tied for GPA, use:
WITH summary AS (
SELECT e.*,
s.name,
DENSE_RANK OVER(PARTITION BY e.cno, e.sectno
ORDER BY s.gpa DESC) AS rank
FROM ENROLL e
JOIN STUDENT s ON s.sid = e.sid)
SELECT s.*
FROM summary s
WHERE s.rank = 1
Hint: consider that there might be more than one student with the highest GPA in a class. An outer query only needs the three fields.
Here are some pointers :-
You are on the right track with your Group By query
This returns you the max GPA for each section based on the cno and sectno fields
Now, you have the Max GPA value for each cno and sectno combination.
Use this data that you have in like a reverse manner if u like to now find all the students matching these combination values.
HINT : Consider the results of your Group By query as a table and Use a INNER JOIN
Even If it is possible that there is more than 1 students for the same max GPA, you will still get them all
Hope this helps!!
This should give you what you are looking for. See Oracle's RANK() function for details on how the GPAs are ranked from highest to lowest by section.
Requirements:
Return a table with the student's name (student.sname) that has the highest gpa in each section (section.cno and section.sectno) as well as all the other attributes from section.
SELECT * FROM
(
SELECT
s.sname,
s.gpa,
sec.dname,
sec.cno,
sec.sectno,
sec.pname,
/* for each "sec.cno, sec.sectno", this will rank each GPA in order from highest to lowest. Ties will have the same rank. */
RANK() OVER(PARTITION BY sec.cno, sec.sectno ORDER BY s.gpa DESC) as r_rank
FROM
enroll e,
student s,
section sec
WHERE
/* join enroll with student */
s.sid = e.sid
/* join section with enroll */
AND sec.dname = e.dname
AND sec.cno = e.cno
AND sec.sectno = e.sectno
)
WHERE r_rank = 1 /* this returns only the highest GPA (maybe multiple students) for each "sec.cno, sec.sectno" combination */
;
Note: If you do not want ties, change RANK() to ROW_NUMBER()
Maybe shortest:
SELECT DISTINCT e.cno, e.sectno , e...,
FIRST_VALUE(s.sname) OVER
(PARTITION BY e.cno, e.sectno ORDER BY s.gpa DESC)
FROM enroll e,
student s
WHERE s.sid = e.sid
Or
SELECT A.*
FROM
( SELECT s._sid, s.sname, e.cno, e.sectno ,..., s.gpa
MAX(s.gpa) OVER (PARTITION BY e.cno, e.sectno) AS maxgpa
FROM enroll e,
student s
WHERE s.sid = e.sid
) A
WHERE A.maxgpa = A.gpa
Although this is answered long back but still I want to present a beautiful explanation , this is very useful for newbie. Also Introduction to SQL has such rules.