table name: country
id country_name
1 USA
2 GERMANY
3 RUSSIA
table name: user
id user_name points country_id
1 user1 20 1
2 user2 10 2
3 user3 11 2
Result should be country-user with maximum points and only country if no user available(3rd record),like below
country_name user_name points
USA user1 20
GERMANY user3 11
RUSSIA (null) (null)
Currently I am using below query but it is sometime taking too much time, like when i have 100000 records.
SELECT c.country_name,u.user_name,u.points FROM country c
LEFT JOIN user u on u.country_id = c.id
WHERE (u.points = (SELECT MAX(points) AS points FROM user WHERE user.id = u.id) OR u.points IS NULL)
So, is there any other way to do it more efficiently, time-wise.
Thanks already!
You can use ROW_NUMBER():
SELECT c.country_name, u.user_name, u.points
FROM country c LEFT JOIN
(SELECT u.*,
ROW_NUMBER() OVER (PARTITION BY u.country_id ORDER BY u.points DESC) as seqnum
FROM user u
WHERE u.points IS NOT NULL
) u
ON u.country_id = c.id AND u.seqnum = 1;
Note: This returns one user per country, even if there are ties for the top one. If you want all of them, use RANK() instead of ROW_NUMBER().
Related
Let's say that i have the following 3 tables :
IDUser Name Surname
1 Lucas Wurth
2 John Charson
3 Erik Drown
IDUser IDLocation
1 1
1 2
2 1
3 2
IDLocation Name
1 Rome
2 Milan
a User Table , a Location table , and a table to assign a location to our users.
I'd like to extract from my database all the users and have a specific column where all assigned locations are reported like so:
IDUser Name Surname Locations
1 Lucas Wurth Rome - Milan
2 John Charson Rome
3 Erik Drown Milan
Note that the user 1 has both Rome & Milan assigned
Currently my query:
SELECT
U.IDUser,
U.Name,
U.Surname,
UL.Name AS LocationName
FROM Users U
LEFT OUTER JOIN UserLocation UL ON
UL.IDUser = U.IDUser
LEFT OUTER JOIN Location L ON
UL.IDLocation = L.IDLocation
Is obviously returning a total of 4 records instead of 3 , is it possible to achievie this using the aggregate function group by? and if so how should i do this?
If you are using SqlServer you can use STRING_AGG :
SELECT
U.IDUser,
U.Name,
U.Surname,
STRING_AGG(UL.Name, ' - ') AS Locations
FROM Users U
LEFT OUTER JOIN UserLocation UL
ON UL.IDUser = U.IDUser
LEFT OUTER JOIN Location L
ON UL.IDLocation = L.IDLocation
GROUP BY U.IDUser, U.Name, U.Surname
I have the following tables:
create table Players (
id integer,
name varchar(50) not null,
birthday date,
memberOf integer not null,
position varchar(20).
primary key (id),
foreign key (memberOf) references Teams(id)
);
create table Goals (
id integer,
scoredIn integer not null,
scoredBy integer not null,
timeScored integer not null,
rating varchar(20),
primary key (id),
foreign key (scoredIn) references Matches(id),
foreign key (scoredBy) references Players(id)
);
create table Teams (
id integer,
country varchar(50) not null,
primary key (id)
);
I have the following data in the above tables:
PLAYERS:
id | name | birthday | memberof | position
7 Mina 1997-01-20 1 Captain
9 John 1997-09-01 1 Quarterback
2 Minnie 1995-10-13 3 Goalkeeper
13 Lisa 1997-03-27 4 Captain
12 Rina 1995-01-03 2 Fullback
11 Jasper 2002-09-22 1 Halfback
17 Rose 1997-02-11 1 Goalkeeper
22 Parvin 1993-03-09 3 Goalkeeper
25 Nasom 1996-12-29 3 Fullback
GOALS:
id | scoredin | scoredby | timescored | rating
1 10 7 60 amazing
2 10 7 30 okay
3 10 7 90 amazing
4 20 9 119 nice
5 20 9 80 amazing
6 20 9 75 amazing
7 30 2 30 nice
8 30 2 90 amazing
9 40 13 110 amazing
TEAMS:
id | country
1 Australia
2 Malaysia
3 Japan
4 Thailand
I am trying to output the country name of the team which has the most players who have never scored a goal. The output should be:
Country | Players
Australia 2
Japan 2
I have the following view, which gives the count of players who have never scored a goal for each country:
create or replace view zerogoals as
select t.country, count(*)
from (
select distinct p.id, p.name, p.memberof, g.scoredby
from players p
full outer join goals g
on p.id = g.scoredby where scoredby is null
) s
inner join teams t on t.id = s.memberof group by t.country;
The above query gives me the following output:
country | count
Australia 2
Japan 2
Malaysia 1
I tried using the max function to get the desired output:
select country, max(count)
from zerogoals
group by country;
However I get the following output:
country | max
Australia 2
Japan 2
Malaysia 1
I am not sure how to get the tuples in the view zerogoals with the maximum value for the attribute count. Any insights are appreciated.
You can use a CTE:
with cte as (
select
t.id, t.country, count(*) players
from teams t inner join (
select * from players
where id not in (select scoredby from goals)
) p on p.memberOf = t.id
group by t.id, t.country
)
select country, players
from cte
where players = (select max(players) from cte)
order by country
See the demo.
Results:
country | players
Australia | 2
Japan | 2
You could try using a inner join between the player, team and the list of not in goals ordered by count and limit to 1
select t.name , count(*)
from player p
INNER JOIN team t ON t.id = p.memberof
inner join (
select p.id
from PLAYERS p
where p.id NOT IN (
select scoredby
from GOALS
) ) t1 on t1.id = p.id
group by t.name
order by count(*) desc
limit 1
if you want all the max then
select t.name , count(*)
from player p
INNER JOIN team t ON t.id = p.memberof
inner join (
select p.id
from PLAYERS p
where p.id NOT IN (
select scoredby
from GOALS
) t1 on t1.id = p.id
group by t.name
having count(*) = (
select t.name , count(*)
from player p
INNER JOIN team t ON t.id = p.memberof
inner join (
select p.id
from PLAYERS p
where p.id NOT IN (
select scoredby
from GOALS
) t1 on t1.id = p.id
group by t.name
order by count(*)
limit 1
)
To get the number of players per country with no goal, you can use:
select t.name, count(*) as num_players_no_goal
from team.t join
player p
on t.id = p.memberof
where not exists (select 1
from goals g
where g.scoredby = p.id
)
group by t.name;
To limit this to just the maximum number, use window functions:
select name, num_players_no_goal
from (select t.name, count(*) as num_players_no_goal,
rank() over (order by count(*) desc) as seqnum
from team.t join
player p
on t.id = p.memberof
where not exists (select 1
from goals g
where g.scoredby = p.id
)
group by t.name
) t
where seqnum = 1;
One slight caveat is that this returns no teams if all players on all teams have scored goals. It is easily modified for that situation, but I'm guessing that you would rather return zero teams than all teams if that were the case.
I am trying to write a query using group by in sub query ,I referred lot of blogs but could not get all the values.
I have three tables and below is the structure of those tables.
Pet_Seller_Master
ps_id ps_name city_id
2 abc 1
3 xyz 2
4 fer 4
5 bbb 1
City_Master
city_id city_name
1 Bangalore
2 COIMBATORE
4 MYSORE
Api_Entry
api_id ps_id otp
1 2 yes
2 3
3 2 yes
4 3 yes
5 4
6 5 yes
7 5 yes
8 5 yes
Query is to get number of sellers, no of pet sellers with zero otp, no of pet sellers with 1 otp, no of pet sellers with 2 otp,no of pet sellers with otp>2 for the particular city and within date range.
Through Below query I am able to get city , psp , and zero otp
select cm.city_name,
count(ps.ps_id) as PSP,
((select count(ps1.ps_id)
FROM ps_master ps1
WHERE ps1.city = cm.city_id)-
(SELECT count(distinct ps1.ps_id)
from ps_master ps1
INNER JOIN api_entry ae ON ps1.ps_id = ae.ps_id and otp!=''
WHERE ps1.city = cm.city_id and date(timestamp) >= curdate() - INTERVAL DAYOFWEEK(curdate())+6 DAY AND date(timestamp) < curdate())) as zero_psp
from ps_master ps INNER JOIN city_master cm ON ps.city = cm.city_id and cm.city_type = 'IN HOUSE PNS'
group by city_id
Please tell me the solution to solve this query.
Thanks in advance
It's not hard to do and you were on a right track. Here is what I would use:
select c.city_name, a.otp, p.ps_name, COUNT(*) nbr
from Api_Entry a
inner join Pet_Seller_Master p on p.ps_id=a.ps_id
inner join City_Master c on p.city_id=c.city_id
group by c.city_name, a.otp, p.ps_name
Now, if you want to get the number of sellers with zero otp, you just apply where clause:
where otp <> 'yes'
If you want to get the number of pet sellers with otp>2, then you just use subquery:
select *
from (
select c.city_name, a.otp, p.ps_name, COUNT(*) nbr
from #tempA a
inner join #tempP p on p.ps_id=a.ps_id
inner join #tempC c on p.city_id=c.city_id
group by c.city_name, a.otp, p.ps_name
) g
where nbr > 2
I have below tables
user table
USER_ID USER_NAME
1 smith
2 clark
3 scott
4 chris
5 john
property table
P_ID PROPERTY
1 first_name
2 last_name
3 age
4 skill
user_property table
PV_ID USER_ID P_ID VALUE
1 1 1 Smith
2 1 2 A
3 1 3 34
4 1 4 Java
5 1 4 DB
6 2 1 Clark
7 2 2 B
8 2 3 39
9 2 4 Java
10 2 4 net
11 2 4 linux
12 3 1 Scott
13 3 2 C
14 3 3 31
I want to write a query which will fetch data from all above tables as below:(Skill will be first skill for that user if available otherwise null)
USER_ID USER_NAME FIRST_NAME LAST_NAME SKILL
1 smith Smith A Java
2 clark Clark B Java
3 scott Scott C null
I have tried like below but getting performance issue:
SELECT
u.user_id,
u.user_name,
MAX(DECODE(p.property, 'first_name', text_value)) firstName,
MAX(DECODE(p.property, 'last_name', text_value)) lastName,
MAX(DECODE(p.property, 'age', text_value)) age,
MAX(DECODE(p.property, 'skill', text_value)) skill
FROM user u,
property p,
user_property up,
WHERE u.user_id = up.user_id
AND p.p_id = up.p_id
GROUP BY u.user_id,
u.user_name;
How could i write this as optimized query for oracle 11g.
The performance of your query depends on the size of the table and on the indexes you have on these tables. It most cases, it is best practice to have an index on each primary and foreign key. The index on the primary key is a must anyway. The index on the foreign key speeds up joins and prevents table locks when you delete rows.
An alternative to your query would be to use more joins instead of subselects and to use the WITH clause to simplify it:
with t as (
select u.user_id, u.user_name, up.p_id, up.value
from user_property up
join user u on u.user_id = up.user_id
)
select u.user_id, u.user_name,
t_first_name.value first_name,
t_last_name.value last_name,
(select min(value) from t where t.user_id = u.user_id and t.p_id = 4) skill
from user u
left join t t_first_name on t_first_name.user_id = u.user_id and t_first_name.p_id = 1
left join t t_last_name on t_last_name.user_id = u.user_id and t_last_name.p_id = 2;
BTW: It's a data model which isn't well suited for SQL. I hope these user properties are the exception and the rest of the database has a cleaner design.
I have tried below query however getting Cartesian product.
with t as (
select u.user_id, u.user_name, up.p_id, up.value
from user_property up
join user u on u.user_id = up.user_id
where u.user_name = 'smith'
)
select u.user_id, u.user_name,
t_first_name.value first_name,
t_last_name.value last_name,
(select min(value) from t where t.user_id = u.user_id and t.p_id = 4) skill
from user u
left join t t_first_name on t_first_name.user_id = u.user_id and t_first_name.p_id = 1
left join t t_last_name on t_last_name.user_id = u.user_id and t_last_name.p_id = 2;
if i execute below query i get 5 as mentioned in my above example (As there are 5 rows in my user_property table for user_id 1 in example)
select count(u.user_id)
from user_property up
join user u on u.user_id = up.user_id
where u.user_name = 'smith'
Hence if i execute below query i get count as 3 as there are 3 rows in my use table example
with t as (
select u.user_id, u.user_name, up.p_id, up.value
from user_property up
join user u on u.user_id = up.user_id
where u.user_name = 'smith'
)
select count(u.user_id)
from user u
left join t t_first_name on t_first_name.user_id = u.user_id and t_first_name.p_id = 1
left join t t_last_name on t_last_name.user_id = u.user_id and t_last_name.p_id = 2;
I have 3 tables:
users:
Id Login
1 John
2 Bill
3 Jim
computers:
Id Name
1 Computer1
2 Computer2
3 Computer3
4 Computer4
5 Computer5
sessions:
UserId ComputerId Minutes
1 2 47
2 1 32
1 4 15
2 5 5
1 2 7
1 1 40
2 5 31
I would like to display this resulting table:
Login Total_sess Total_min Most_freq_computer Sess_on_most_freq Min_on_most_freq
John 4 109 Computer2 2 54
Bill 3 68 Computer5 2 36
Jim - - - - -
Myself I can only cover first 3 columns with:
SELECT Login, COUNT(sessions.UserId), SUM(Minutes) FROM users
LEFT JOIN sessions
ON users.Id = sessions.UserId GROUP BY users.Id
And some kind of other columns with:
SELECT main.*
FROM (SELECT UserId, ComputerId, COUNT(*) AS cnt ,SUM(Minutes)
FROM sessions
GROUP BY UserId, ComputerId) AS main
INNER JOIN (
SELECT ComputerId, MAX(cnt) AS maxCnt FROM (
SELECT ComputerId, UserId, COUNT(*) AS cnt FROM sessions GROUP BY ComputerId, UserId
)
AS Counts GROUP BY ComputerId)
AS maxes
ON main.ComputerId = maxes.ComputerId
AND main.cnt = maxes.maxCnt
But I need to get whole resulting table in one query. I feel I'm doing something completely wrong. Need help.
Here you are:
SELECT u.login, t1.total_sess, t1.total_min, t2.mf, t2.sess_mf, t2.min_mf
FROM users u
LEFT JOIN (
SELECT userid, COUNT(minutes) AS total_sess, SUM(minutes) AS total_min
FROM sessions
GROUP BY userid
) AS t1 ON t1.userid = u.id
LEFT JOIN (
SELECT userid, name AS mf, COUNT(*) AS sess_mf, SUM(minutes) AS min_mf
FROM sessions s
JOIN computers c ON c.id = s.computerid
GROUP BY userid, computerid
HAVING COUNT(computerid) >= ALL(SELECT COUNT(*)
FROM sessions s2
WHERE s2.userid = s.userid
GROUP BY s2.computerid)
) AS t2 ON t2.userid = u.id
I'm using MySQL syntax, but it should be pretty portable.
If you need anything more, feel free to ask!
EDIT: I updated the query, the previous one was wrong :(