I want to fetch the first row where foreign key match. I don't know how to select first row
where foreign key matches
events table
id | name
----------------
1 | john
----------------
2 | Cat
event_attendee table
id | event_id | type
--------------------------
1 | 1 | User
--------------------------
2 | 1 | Local
--------------------------
3 | 1 | User
--------------------------
4 | 2 | User
--------------------------
5 | 2 | User
I want this result
id | name | event_id | type
------------------------------------
1 | John | 1 | User
------------------------------------
2 | Cat | 2 | User
Tried
select
a.*,
b.*
from
events as a
left join (
select
distinct
event_attendee.events_id,
event_attendee.type
from
event_attendee
left join events on
event_attendees.events_id = events.id
where
events.id = event_attendees.events_id
limit 1
) as b on
a.id = b.events_id
Problem
It only works for the 1st row, for 2nd row its show empty
id | name | type
------------------------------------
1 | John | User
------------------------------------
2 | Cat |
You can do this using a lateral join. In Postgres, the syntax is:
select e.*, ea.*
from events e left join lateral
(select ea.event_Id, ea.Type
from event_attendee ea
where ea.event_id = e.id
order by ea.id
) ea
on 1=1;
However, distinct on is a way to do this with no subqueries:
select distinct on (e.event_id) e.*, ea.*
from events e join
event_attendee ea
on ea.event_id = e.id
order by e.event_id, ea.id;
I would expect the lateral join to work better on larger tables, particularly with the correct indexes.
This is easy with a cross apply:
select *
from events e
cross apply (
select top (1) event_Id, Type
from event_attendee ea
where ea.event_id=e.id
order by id
)x
Edit, alternative compatible method!
select e.*,ea.event_Id, (select type from event_attendee ea2 where ea2.id=ea.id ) Type
from (
select Min(id) Id, event_id
from event_attendee
group by event_id
)ea
join events e on e.id=ea.event_id
One way to get the rank and use it to filter 1st record:
select
t_.id, t_.name, t_.type
from
(
select a.*, b.type,
rank() OVER (PARTITION BY a.id ORDER BY b.id asc) rank_
from events a
left join event_attendees b
on
a.id = b.events_id
) t_
where
t_.rank_ = 1
Related
I have two tables:
Table A
ID | name
---+----------
1 | example
2 | example2
Table B (created field is timestamptz)
ID | id_table_a | dek | created
---+------------+------+---------------------
1 | 1 | deka | 2019-10-21 10:00:00
2 | 2 | dekb | 2019-10-21 11:00:00
3 | 1 | dekc | 2019-10-21 09:00:00
4 | 2 | dekd | 2019-10-21 09:40:00
5 | 1 | deke | 2019-10-21 09:21:00
I need to get records from Table A and each records should have the last dek from table b based on created.
How can I do that?
I would use a lateral join, very often this is faster than using a select max()
select a.*, b.dek
from table_a a
join lateral (
select id, id_table_a, dek, created
from table_b
where b.id_table_a = a.id
order by created desc
limit 1
) tb on true;
Another alternative is to use distinct on:
select a.*, b.dek
from table_a a
join lateral (
select distinct on (id_table_a) id, id_table_a, dek, created
from table_b
order by id_table_a, created desc
) tb on tb.id_table_a = a.id;
It depends on your data distribution which one is faster.
With a CTE returning the joined tables and NOT EXISTS:
with cte as (
select a.id, a.name, b.dek, b.created
from tablea a inner join tableb b
on b.id_table_a = a.id
)
select t.* from cte t
where not exists (
select 1 from cte
where id = t.id and created > t.created
)
There are 2 tables, users and job_experiences.
I want to return a list of all job_experiences except the first associated with each user.
users
id
---
1
2
3
job_experiences
id | start_date | user_id
--------------------------
1 | 201001 | 1
2 | 201201 | 1
3 | 201506 | 1
4 | 200901 | 2
5 | 201005 | 2
Desired result
id | start_date | user_id
--------------------------
2 | 201201 | 1
3 | 201506 | 1
5 | 201005 | 2
Current query
select
*
from job_experiences
order by start_date asc
offset 1
But this doesn't work as it would need to apply the offset to each user individually.
You can do this with a lateral join:
select je.*
from users u cross join lateral
(select je.*
from job_experiences je
where u.id = je.user_id
order by id
offset 1 -- all except the first
) je;
For performance, an index on job_experiences(user_id, id) is recommended.
use row_number() window function
with cte as
(
select e.*,
row_number()over(partition by user_id order by start_date desc) rn,
count(*) over(partition by user_id) cnt
from users u join job_experiences e on u.id=e.user_id
)
, cte2 as
(
select * from cte
) select * from cte2 t1
where rn<=(select max(cnt)-1 from cte2 t2 where t1.user_id=t2.user_id)
You could use an intermediate CTE to get the first (MIN) jobs for each user, and then use that to determine which records to exclude:
WITH user_first_je("user_id", "job_id") AS
(
SELECT "user_id", MIN("id")
FROM job_experiences
GROUP BY "user_id"
)
SELECT job_experiences.*
FROM job_experiences
LEFT JOIN user_first_je ON
user_first_je.job_id = job_experiences.id
WHERE user_first_je.job_id IS NULL;
I have the following tables:
event_tbl
| event_id (PK) | event_date | event_location |
|---------------|------------|----------------|
| 1 | 01/01/2018 | Miami |
| 2 | 02/04/2018 | Tampa |
performer_tbl
| performer_id (PK) | event_id (FK) | genre |
|-------------------|---------------|-------|
| 1 | 1 | A |
| 2 | 1 | B |
| 3 | 2 | A |
| 4 | 2 | C |
I want to find events that have both genre A and genre B (should just return event 1), and I'm lost on writing the query. Maybe I just haven't had enough coffee, but all I can come up with is doing two derived columns with a case statement that count either genre and group by the event_id, then filtering both to >0. It just doesn't seem very elegant.
This should do the job (in MySQL, for other DBMS the syntax can be varied easily):
SELECT
e.event_id
FROM
event_tbl e
JOIN performer_tbl p USING(event_id)
GROUP BY e.event_id
HAVING SUM(IF(p.genre = 'A', 1, 0)) >= 1 AND SUM(IF(p.genre = 'B', 1, 0)) >= 1;
if you are using sql server, check below:
Select * From
event_tbl
where event_id
IN
(
select event_id
from performer_tbl as A
where exists (select 1
from perfoermer_tbl as B
where B.event_id = A.event_id and B.genre = 'A')
and
exists (select 1
from perfoermer_tbl as B
where B.event_id = A.event_id and B.genre = 'B')
)
This should work in any SQL database (at least in mysql, sql server, postgres or oracle)
select event_tbl.* FROM (
select event_id
from performer_tbl
where genre = 'A'
GROUP BY event_id) a_t
INNER JOIN (select event_id
from performer_tbl
where genre = 'B'
GROUP BY event_id) b_t
ON a_t.event_id = b_t.event_id
INNER JOIN event_tbl
ON event_tbl.event_id = a_t.event_id
This also works using left joins: (Since there are no function calls or sub-selects, it is fast. Also, it's usable in most SQL engines.)
SELECT DISTINCT
p1.event_id
,e.event_date
,e.event_location
FROM
performer_tbl as p1
inner join event_tbl as e on
p1.event_id = e.event_id
left outer join performer_tbl as p2 on
p1.event_id = p2.event_id
AND p2.genre = 'A'
left outer join performer_tbl as p3 on
p1.event_id = p3.event_id
AND p3.genre = 'B'
WHERE
p2.genre IS NOT NULL
AND p3.genre IS NOT NULL;
If I correctly understand what you need, you can try this:
Select *
from event_tbl e
where exists (select *
from performer_tbl p
where p.event_id = e.event_id
and p.genre in ('A', 'B'))
I'm writing a DB view that pulls data from several tables. The goal is to determine the latest status of a company, and this is noted by each record (grouped by company_id) with the highest vetting_event_type_position.
Essentially I'm trying to grab the latest record for each company. I'm not a SQL guru at all; I understand I need to group by in order to collapse the related records, but I can't get that to work.
Current results
company_id | name | ... | vetting_event_type_position
-----------------------------------------------------
1 | ABC | ... | 1
1 | ABC | ... | 2
1 | ABC | ... | 3
2 | CBS | ... | 1
2 | CBS | ... | 2
3 | HBO | ... | 1
DESIRED results
company_id | name | ... | vetting_event_type_position
-----------------------------------------------------
1 | ABC | ... | 3
2 | CBS | ... | 2
3 | HBO | ... | 1
SQL Code
SELECT
companies.id as company_id,
companies.name as name,
companies.uuid as uuid,
companies.company_type as company_type,
companies.description as overview,
practice_areas.id as practice_area_id,
practice_areas.name as practice_area_name,
companies.created_at as created_at,
companies.updated_at as updated_at,
companies.created_by as created_by,
companies.updated_by as updated_by,
vettings.id as vetting_id,
vettings.name as vetting_name,
vetting_event_types.name as vetting_event_status,
vetting_events.id as vetting_event_id,
vetting_event_types.position as vetting_event_type_position
FROM
vettings
LEFT OUTER JOIN vetting_events ON (vettings.id = vetting_events.vetting_id)
LEFT OUTER JOIN vetting_event_types ON (vetting_events.vetting_event_type_id = vetting_event_types.id)
RIGHT OUTER JOIN companies ON (companies.id = vettings.company_id)
LEFT OUTER JOIN practice_areas ON (companies.practice_area_id = practice_areas.id)
LEFT OUTER JOIN dispositions ON (companies.disposition_id = dispositions.id)
ORDER BY
name, vetting_name, vetting_event_type_position
;
Associations among tables
companies has_many vettings
vettings has_many vetting_events
vetting_events belongs_to vetting_event_types
or put another way...
companies -> vettings -> vetting_events <- vetting_event_types
I am trying to retrieve the company record with the highest vetting_event_types.position value for each group.
SELECT company_id
,name
,uuid
,company_type
,overview
,practice_area_id
,practice_area_name
,created_at
,created_by
,updated_by
,vetting_id
,vetting_name
,vetting_event_status
,vetting_event_id
,vetting_event_type_position
FROM (
SELECT
companies.id as company_id,
companies.name as name,
companies.uuid as uuid,
companies.company_type as company_type,
companies.description as overview,
practice_areas.id as practice_area_id,
practice_areas.name as practice_area_name,
companies.created_at as created_at,
companies.updated_at as updated_at,
companies.created_by as created_by,
companies.updated_by as updated_by,
vettings.id as vetting_id,
vettings.name as vetting_name,
vetting_event_types.name as vetting_event_status,
vetting_events.id as vetting_event_id,
vetting_event_types.position as vetting_event_type_position,
ROW_NUMBER() OVER (PARTITION BY companies.id ORDER BY vetting_event_types.position DESC) rn
FROM vettings
LEFT OUTER JOIN vetting_events ON (vettings.id = vetting_events.vetting_id)
LEFT OUTER JOIN vetting_event_types ON (vetting_events.vetting_event_type_id = vetting_event_types.id)
RIGHT OUTER JOIN companies ON (companies.id = vettings.company_id)
LEFT OUTER JOIN practice_areas ON (companies.practice_area_id = practice_areas.id)
LEFT OUTER JOIN dispositions ON (companies.disposition_id = dispositions.id)
) A
WHERE A.rn = 1
ORDER BY name, vetting_name, vetting_event_type_position
You can use row_number analytic function.
Select * from (
Select ...,
Row_number() over ( partition by company_id order by vetting_event_type_position desc) as seq) T
Where seq=1
Firstly, I apologize for my English. I want get auctions with count of bids and buys. It should look like this:
id | name | bids | buys
-----------------------
1 | Foo | 4 | 1
2 | Bar | 0 | 0
I have tables like following:
auction:
id | name
---------
1 | Foo
2 | Bar
auction_bid:
id | auction_id
---------------
1 | 1
2 | 1
3 | 1
4 | 1
auction_buy:
id | auction_id
---------------
1 | 1
I can get numbers in two queries:
SELECT *, COUNT(abid.id) AS `bids` FROM `auction` `t` LEFT JOIN auction_bid abid ON (t.id = abid.auction) GROUP BY t.id
SELECT *, COUNT(abuy.id) AS `buys` FROM `auction` `t` LEFT JOIN auction_buy abuy ON (t.id = abuy.auction) GROUP BY t.id
But when i combined it into one:
SELECT *, COUNT(abid.id) AS `bids`, COUNT(abuy.id) AS `buys` FROM `auction` `t` LEFT JOIN auction_bid abid ON (t.id = abid.auction) LEFT JOIN auction_buy abuy ON (t.id = abuy.auction) GROUP BY t.id
It was returning wrong amount (bids as much as buys).
How to fix this and get counts in one query?
You'll need to count DISTINCT abuy and abid IDs to eliminate the duplicates;
SELECT t.id, t.name,
COUNT(DISTINCT abid.id) `bids`,
COUNT(DISTINCT abuy.id) `buys`
FROM `auction` `t`
LEFT JOIN auction_bid abid ON t.id = abid.auction_id
LEFT JOIN auction_buy abuy ON t.id = abuy.auction_id
GROUP BY t.id, t.name;
An SQLfiddle to test with.
Try this:
SELECT t.*,COUNT(abid.id) as bids,buys
FROM auction t LEFT JOIN
auction_bid abid ON t.id = abid.auction_id LEFT JOIN
(SELECT t.id, Count(abuy.id) as buys
FROM auction t LEFT JOIN
auction_buy abuy ON t.id = abuy.auction_id
GROUP BY t.id) Temp ON t.id=Temp.id
GROUP BY t.id
Result:
ID NAME BIDS BUYS
1 Foo 2 0
2 Bar 1 1
Result in SQL Fiddle.