I have these 3 tables and I am trying to count, how many "hints" and "quizzes" are there for specific town id.
db_town
id
town
1
New York
db_hint
id
town_id
hint
1
1
test
db_quiz
id
town_id
quiz
1
1
quiz 1
2
1
quiz 2
I am using this statement, but it does not work :(
SELECT count(q.id),count(h.id) FROM `db_town` t LEFT JOIN `db_quiz` q ON t.id = q.town_id LEFT JOIN `db_hint` h ON t.id = h.town_id WHERE t.id = 1 GROUP BY t.id
and it produces this result:
count(q.id)
count(h.id)
2
2
Do I need to use two statements? Or is it possible to query it in a single SQL statement? I am using MariaDB.
You can use union all and aggregation:
select town_id, sum(is_hint), sum(is_quiz)
from ((select town_id, 1 as is_hint, 0 as is_quiz
from hints
) union all
(select town_id, 0, 1
from quizzes
)
) t
group by town_id;
Alternatively, you can use correlated subqueries:
select t.*,
(select count(*) from hints h where h.town_id = t.id),
(select count(*) from quizzes q where q.town_id = t.id)
from towns t;
Two things to look out for:
JOINs are likely to multiply rows and throw off the counts.
Getting 0 values if a town has no hints or quizzes.
You can use COUNT (DISTINCT) if both the hint id and the quiz id are unique.
SELECT
count(distinct q.id),count(distinct h.id)
FROM `db_town` t
LEFT JOIN `db_quiz` q ON t.id = q.town_id
LEFT JOIN `db_hint` h ON t.id = h.town_id
WHERE t.id = 1 GROUP BY t.id
Related
I have three tables where the bold attribute(s) is the primary key
Restaurants(restaurant_ID, name, ...)
resturant_ID, name, ...
1, Macdonalds
2, Hubert
3, Dorsia
... ...
Identifier(restaurant_ID, food_ID)
restaurant_ID, food_ID, ...
1, 1
1, 4
2, 1
2, 7
... ...
Food(food_ID, name, ...)
food_ID food_name
1 Chips
2 Burgers
3 Salmon
... ...
Using postgres I want to list out all restaurants (restaurant_id and name - 1 row per restaurant) that have share the exact same set of foods with at least one other restaurant.
For example, let's say
Restaurant with ID "1" has only associated food_id's 1 and 4 as shown in Identifier
Restaurant with ID "3" has only associated food_id's 4 and 1 as shown in Identifier
Restaurant with ID "7" has only associated food_id's 6 as shown in Identifier
Restaurant with ID "9" has only associated food_id's 6 as shown in Identifier
Then output
Restaurant_id name
1 name1
3 name3
7 ...
9 ...
Any help would be greatly appreciated!
Thank you
Use the aggregate function string_agg() to get the full list of foods for each restaurant:
with cte as (
select restaurant_ID,
string_agg(food_ID::varchar(10),',' order by food_ID) foods
from identifier
group by restaurant_ID
)
select r.*
from Restaurants r inner join cte c
on c.restaurant_ID = r.restaurant_ID
where exists (select 1 from cte where restaurant_ID <> c.restaurant_ID and foods = c.foods)
But I would prefer to group restaurants based on matching foods:
with cte as (
select restaurant_ID,
string_agg(food_ID::varchar(10),',' order by food_ID) foods
from identifier
group by restaurant_ID
)
select string_agg(r.name, ',') restaurants
from Restaurants r inner join cte c
on c.restaurant_ID = r.restaurant_ID
group by foods
having count(*) > 1
See the demo.
Here is a way to get the unique set of resturants having exactly same food items. This uses array_agg() and array_to_string() functions
With cte as
(select T.restaurant_id, array_to_string(array_agg(food_id), ',') as food_list
from
(select *
from Identifier t1
order by restaurant_id, food_id) T
group by T.restaurant_id)
select
concat(r1.name,',',r2.name) as resturant_names,
t1.restaurant_id as restaurant_id1,
r1.name as restaurant_1,
t2.restaurant_id as restaurant_id2,
r2.name as restaurant_2,
t1.food_list as common_food_ids
from cte t1
join cte t2
on t1.restaurant_id < t2.restaurant_id
and t1.food_list = t2.food_list
left join Restaurants r1
on t1.restaurant_id = r1.restaurant_id
left join Restaurants r2
on t2.restaurant_id = r2.restaurant_id;
EDIT : Here is a dB fiddle - https://dbfiddle.uk/?rdbms=postgres_12&fiddle=e2de05edfbe036cc0d81c64d60f0b599 . Also, just for reference, solution to the same problem in Oracle using listagg function - https://dbfiddle.uk/?rdbms=oracle_11.2&fiddle=12785c3d5abbca97be5d44dd45a6da4a
Update : Below query addresses the update output format of the question.
With cte as
(select T.restaurant_id, array_to_string(array_agg(food_id), ',') as food_list
from
(select *
from Identifier t1
order by restaurant_id, food_id) T
group by T.restaurant_id)
select
--concat(r1.name,',',r2.name) as resturant_names,
t1.restaurant_id as restaurant_id,
r1.name as restaurant--,
--t2.restaurant_id as restaurant_id2,
--r2.name as restaurant_2,
--t1.food_list as common_food_ids
from cte t1
join cte t2
on t1.restaurant_id = t2.restaurant_id
and t1.food_list = t2.food_list
left join Restaurants r1
on t1.restaurant_id = r1.restaurant_id
left join Restaurants r2
on t2.restaurant_id = r2.restaurant_id;
As I understand your question, you want all restaurants that have the same list of foods as restaurant 1.
If so, that's a relation division problem. Here is an approach using joins and aggregation:
select r.name
from identifier i1
inner join identifier i2 on i2.food_id = i1.food_id
inner join restaurant r on r.restaurant_id = i2.restaurant_id
where i1.restaurant_id = 1
group by r.restaurant_id
having count(*) = (select count(*) from identifier i3 where i3.restaurant_id = 1)
How to find the user with the most referrals that have at least three blue shoes using PostgreSQL?
table 1 - users
name (matches shoes.owner_name)
referred_by (foreign keyed to users.name)
table 2 - shoes
owner_name (matches persons.name)
shoe_name
shoe_color
What I have so far is separate queries returning parts of what I want above:
(SELECT count(*) as shoe_count
FROM shoes
GROUP BY owner_name
WHERE shoe_color = “blue”
AND shoe_count>3) most_shoes
INNER JOIN
(SELECT count(*) as referral_count
FROM users
GROUP BY referred_by
) most_referrals
ORDER BY referral_count DESC
LIMIT 1
Two subqueries seem like the way to go. They would look like:
SELECT s.owner_name, s.show_count, r.referral_count
FROM (SELECT owner_name, count(*) as shoe_count
FROM shoes
WHERE shoe_color = 'blue'
GROUP BY owner_name
HAVING shoe_count >= 3
) s JOIN
(SELECT referred_by, count(*) as referral_count
FROM users
GROUP BY referred_by
) r
ON s.owner_name = r.referred_by
ORDER BY r.referral_count DESC
LIMIT 1 ;
Given tables, Profiles, and Memberships where a profile has many memberships, how do I query profiles based on the number of memberships?
For example I want to get the number of profiles with 2 memberships. I can get the number of profiles for each membership with:
SELECT "memberships"."profile_id", COUNT("profiles"."id") AS "membership_count"
FROM "profiles"
INNER JOIN "memberships" on "profiles"."id" = "memberships"."profile_id"
GROUP BY "memberships"."profile_id"
That returns results like
profile_id | membership_count
_____________________________
1 2
2 5
3 2
...
But how do I group and sum the counts to get the query to return results like:
n | profiles_with_n_memberships
_____________________________
1 36
2 28
3 29
...
Or even just a query for a single value of n that would return
profiles_with_2_memberships
___________________________
28
I don't have your sample data, but I just recreated the scenario here with a single table : Demo
You could LEFT JOIN the counts with generate_series() and get zeroes for missing count of n memberships. If you don't want zeros, just use the second query.
Query1
WITH c
AS (
SELECT profile_id
,count(*) ct
FROM Table1
GROUP BY profile_id
)
,m
AS (
SELECT MAX(ct) AS max_ct
FROM c
)
SELECT n
,COUNT(c.profile_id)
FROM m
CROSS JOIN generate_series(1, m.max_ct) AS i(n)
LEFT JOIN c ON c.ct = i.n
GROUP BY n
ORDER BY n;
Query2
WITH c
AS (
SELECT profile_id
,count(*) ct
FROM Table1
GROUP BY profile_id
)
SELECT ct
,COUNT(*)
FROM c
GROUP BY ct
ORDER BY ct;
here is my data
movies table:
id title
10 Promise Land
13 Alive
14 Bruce Almighty
15 Decay
19 Malcom X
users table:
id username
1 Franck
2 Matt
archive table:
userid movieid
1 13
2 14
1 14
I'd like to get all the movies.id, movies.title that are not in the archive table for user id = 1.
I want to use JOINS (I don't want a select of select)
result should be:
id title
10 Promise Land
15 Decay
19 Malcom X
the following SQL fails:
SELECT a.id,a.title
FROM db.movies AS a
LEFT JOIN db.archive AS b ON a.id = b.movieid
LEFT JOIN db.users AS c ON c.id = b.userid
WHERE b.movieid IS NULL OR b.userid !=1;
Thanks
Using JOINS. You put the userid filter into the JOIN
SELECT
a.id,a.title
FROM
binews.movies AS a
LEFT JOIN
binews.archive AS b ON a.id = b.movieid AND b.userid <> 1
WHERE
b.movieid IS NULL;
However, you are actually asking "give my movies where they don't exists for this user in the archive table)
SELECT
a.id,a.title
FROM
binews.movies AS a
WHERE
NOT EXISTS (SELECT *
FROM
binews.archive AS b
WHERE
a.id = b.movieid AND b.userid <> 1);
This is more correct generally. In some cases you'll get multiple rows from a LEFT JOIN where a userid has used the same more than once. To correct this, you'll need DISTINCT which adds processing.
However, EXISTS removes this multiple row output.
See this for more: http://explainextended.com/2009/09/15/not-in-vs-not-exists-vs-left-join-is-null-sql-server/
In SQLServer2005+ you can use option with EXISTS and EXCEPT operators
SELECT *
FROM dbo.movies
WHERE EXISTS (
SELECT id
EXCEPT
SELECT movieid
FROM archive
WHERE userid = 1
)
Demo on SQLFiddle
OR option with NOT EXISTS AND INTERSECT operators
SELECT *
FROM dbo.movies
WHERE NOT EXISTS (
SELECT movieid
FROM archive
WHERE userid = 1
INTERSECT
SELECT id
)
Demo on SQLFiddle
select * from binews.movies
where id not in(select movieid from binews.archive where userid<>1 )
thanks to gbn. here is the solution with a correction "AND b.userid=1"
SELECT
a.id,a.title
FROM
binews.movies AS a
LEFT JOIN
binews.archive AS b ON a.id = b.movieid AND b.userid=1
WHERE
b.movieid IS NULL
I'm trying to make a query that looks at a single table to see if a student is in a team called CMHT and in a medic team - if they are I don't want to see the result.
I only want see the record if they're only in CMHT or medic, not both.
Would the right direction be using sub query to filter it out? I've done a search on NOT IN but how could you get to see check if its in more then 2 teams are not?
Student Team ref
1 CMHT 1
1 Medic 2
2 Medic 3 this would be in the result
3 CMHT 5 this would be in the result
So far I've done the following code would I need use a sub query or do a self join and filter it that way?
SELECT Table1.Student, Table1.Team, Table1.refnumber
FROM Table1
WHERE (((Table1.Team) In ('Medics','CMHT'))
This is Mark Byers's answer with a HAVING clause instead of a subquery:
SELECT Student, Team, ref
FROM Table1
GROUP BY Student
HAVING COUNT(Student) = 1
SELECT *
FROM students
WHERE NOT EXISTS
(
SELECT NULL
FROM students si
WHERE si.student = s.student
AND si.team = 'CMHT'
)
OR NOT EXISTS
(
SELECT NULL
FROM students si
WHERE si.student = s.student
AND si.team = 'Medic'
)
SELECT a.*
FROM Table1 a
INNER JOIN
( SELECT Student, COUNT(*) FROM Table1
GROUP BY Student
HAVING COUNT(*) = 1)b
ON (a.Student = b.Student)
how could you get to see check if its in 2 or more teams?
You can count the number of teams per student and then filter only those you want to see:
SELECT student FROM
(
SELECT student, COUNT(*) AS cnt
FROM Table1
GROUP BY student
) T1
WHERE cnt = 1
You can do it with outer join
select COALESCE(t1.Student, t2.Student) as Student,
COALESCE(t1.Team, t2.Team) as Team,
COALESCE(t1.ref, t2.ref) as ref
from
(select * from Student where Team = 'CMHT') t1
outer join
(select * from Student where Team = 'Medic') t2
on t1.Student = t2.Student
where
t1.Student is null or
t2.Student is null;