I have this SQL:
select * from `posts`
where `posts`.`deleted_at` is null
and `expire_at` >= '2017-03-26 21:23:42.000000'
and (
select count(distinct tags.id) from `tags`
inner join `post_tag` on `tags`.`id` = `post_tag`.`tag_id`
where `post_tag`.`post_id` = `posts`.`id`
and (`tags`.`tag` like 'PHP' or `tags`.`tag` like 'pop' or `tags`.`tag` like 'UI')
) >= 1
Is it possible order the results by number of tags in posts?
Maybe add there alias?
Any information can help me.
Convert your correlated subquery into a join:
select p.*
from posts p
join (
select pt.post_id,
count(distinct t.id) as tag_count
from tags t
inner join post_tag pt on t.id = pt.tag_id
where t.tag in ('PHP', 'pop', 'UI')
group by pt.post_id
) pt on p.id = pt.post_id
where p.deleted_at is null
and p.expire_at >= '2017-03-26 21:23:42.000000'
order by pt.tag_count desc;
Also, note that I changed the bunch of like and or to single IN because you are not matching any pattern i.e. there is no % in the string. So, better using single IN instead.
Also, if you have defined your table names, column names etc keeping keywords etc in mind, you shouldn't have the need to use the backticks. They make reading a query difficult.
Related
There is an example request in which there are several joins.
SELECT DISTINCT ON(a.id_1) 1, a.name, b.task, c.created_at
FROM a
INNER JOIN b ON a.id_2 = b.id
INNER JOIN c ON a.ID_2 = c.id
WHERE a.deleted_at IS NULL
ORDER BY a.id_1 desc
In this case, the query will work, sorting by unique values of id_1 will take place. But I need to sort by the column a.name. In this case, postresql will swear with the words ERROR: SELECT DISTINCT ON expressions must match initial ORDER BY expressions.
The following query can serve as a solution to the problem:
SELECT *
FROM(
SELECT DISTINCT ON(a.id_1) a.name, b.task, c.created_at
FROM a
INNER JOIN b ON a.id_2 = b.id
INNER JOIN c ON a.ID_2 = c.id
WHERE a.deleted_at IS NULL
)
ORDER_BY a.name desc
But in reality the database is very large and such a query is not optimal. Are there other ways to sort by the selected column while keeping one uniqueness?
My query is below:
select
u.Id,
STRING_AGG(sf.Naziv, ', ') as 'Ustrojstvena jedinica',
ISNULL(CONVERT(varchar(200), (STRING_AGG(TRIM(p.Naziv), ', ')), 121), '')
as 'Partner',
from Ugovor as u
left join VezaUgovorPartner as vup
on vup.UgovorId = u.Id AND vup.IsDeleted = 'false'
left join [TEST_MaticniPodaci2].dbo.Partner as p
on p.PartnerID = vup.PartnerId
left join [dbo].[VezaUgovorUstrojstvenaJedinica] as vuu
on vuu.UgovorId = u.Id
left join [TEST_MaticniPodaci2].hcphs.SifZavod as sf
on sf.Id = vuu.UstrojstvenaJedinicaId
left join [dbo].[SifVrstaUgovora] as vu
on u.VrstaUgovoraId = vu.Id
group by u.Id, sf.Naziv
My problem is that I can have more sf.Naziv and also only one sf.Naziv so I have to check if there is one and then show only one result and if there is two or more to show more results. But for now the problem is when I have only one sf.Naziv, query returns two sf.Naziv with the same name because in first STRING_AGG i have more records about p.Naziv.
I have no idea how to implement DISTINCT into STRING_AGG function
Any other solutions are welcome, but I think it should work with DISTINCT function.
It looks like distinct won't work, so what you should do is put your whole query in a subquery, remove the duplicates there, then do STRING_AGG on the data that has no duplicates.
SELECT STRING_AGG(data)
FROM (
SELECT DISTINCT FROM ...
)
I like this format for distinct values:
(d is required but you can use any variable name there)
SELECT STRING_AGG(LoadNumber, ',') as LoadNumbers FROM (SELECT DISTINCT LoadNumber FROM [ASN]) d
A sample query to remove duplicates while using STRING_AGG().
WITH cte AS (
SELECT DISTINCT product
FROM activities
)
SELECT STRING_AGG(product, ',') products
FROM cte;
Or you can use the following query. The result is same -
SELECT STRING_AGG(product, ',') as products
from (
SELECT product
FROM Activities
GROUP BY product
) as _ ;
I have a simple query:
SELECT * FROM Products p
LEFT JOIN SomeTable st ON st.SomeId = p.SomeId AND st.SomeOtherId = p.SomeOtherId
So far so good.
But the first join to SomeId can be NULL, In that case the check should be IS NULL, and that's where the join fails. I tried to use a CASE, but can't get that to work also.
Am I missing something simple here?
From Undocumented Query Plans: Equality Comparisons.
SELECT *
FROM Products p
LEFT JOIN SomeTable st
ON st.SomeOtherId = p.SomeOtherId
AND EXISTS (SELECT st.SomeId INTERSECT SELECT p.SomeId)
In SQL Server, I know for sure that the following query;
SELECT things.*
FROM things
LEFT OUTER JOIN (
SELECT thingreadings.thingid, reading
FROM thingreadings
INNER JOIN things on thingreadings.thingid = things.id
ORDER BY reading DESC LIMIT 1) AS readings
ON things.id = readings.thingid
WHERE things.id = '1'
Would join against thingreadings only once the WHERE id = 1 had restricted the record set down. It left joins against just one row. However in order for performance to be acceptable in postgres, I have to add the WHERE id= 1 to the INNER JOIN things on thingreadings.thingid = things.id line too.
This isn't ideal; is it possible to force postgres to know that what I am joining against is only one row without explicitly adding the WHERE clauses everywhere?
An example of this problem can be seen here;
I am trying to recreate the following query in a more efficient way;
SELECT things.id, things.name,
(SELECT thingreadings.id FROM thingreadings WHERE thingid = things.id ORDER BY id DESC LIMIT 1),
(SELECT thingreadings.reading FROM thingreadings WHERE thingid = things.id ORDER BY id DESC LIMIT 1)
FROM things
WHERE id IN (1,2)
http://sqlfiddle.com/#!15/a172c/2
Not really sure why you did all that work. Isn't the inner query enough?
SELECT t.*
FROM thingreadings tr
INNER JOIN things t on tr.thingid = t.id AND t.id = '1'
ORDER BY tr.reading DESC
LIMIT 1;
sqlfiddle demo
When you want to select the latest value for each thingID, you can do:
SELECT t.*,a.reading
FROM things t
INNER JOIN (
SELECT t1.*
FROM thingreadings t1
LEFT JOIN thingreadings t2
ON (t1.thingid = t2.thingid AND t1.reading < t2.reading)
WHERE t2.thingid IS NULL
) a ON a.thingid = t.id
sqlfiddle demo
The derived table gets you the record with the most recent reading, then the JOIN gets you the information from things table for that record.
The where clause in SQL applies to the result set you're requesting, NOT to the join.
What your code is NOT saying: "do this join only for the ID of 1"...
What your code IS saying: "do this join, then pull records out of it where the ID is 1"...
This is why you need the inner where clause. Incidentally, I also think Filipe is right about the unnecessary code.
How would I redesign the below query so that it will recursively loop through entire tree to return all descendants from root to leaves? (I'm using SSMS 2008). We have a President at the root. under him are the VPs, then upper management, etc., on down the line. I need to return the names and titles of each. But this query shouldn't be hard-coded; I need to be able to run this for any selected employee, not just the president. This query below is the hard-coded approach.
select P.staff_name [Level1],
P.job_title [Level1 Title],
Q.license_number [License 1],
E.staff_name [Level2],
E.job_title [Level2 Title],
G.staff_name [Level3],
G.job_title [Level3 Title]
from staff_view A
left join staff_site_link_expanded_view P on P.people_id = A.people_id
left join staff_site_link_expanded_view E on E.people_id = C.people_id
left join staff_site_link_expanded_view G on G.people_id = F.people_id
left join facility_view Q on Q.group_profile_id = P.group_profile_id
Thank you, this was most closely matching what I needed. Here is my CTE query below:
with Employee_Hierarchy (staff_name, job_title, id_number, billing_staff_credentials_code, site_name, group_profile_id, license_number, region_description, people_id)
as
(
select C.staff_name, C.job_title, C.id_number, C.billing_staff_credentials_code, C.site_name, C.group_profile_id, Q.license_number, R.region_description, A.people_id
from staff_view A
left join staff_site_link_expanded_view C on C.people_id = A.people_id
left join facility_view Q on Q.group_profile_id = C.group_profile_id
left join regions R on R.regions_id = Q.regions_id
where A.last_name = 'kromer'
)
select C.staff_name, C.job_title, C.id_number, C.billing_staff_credentials_code, C.site_name, C.group_profile_id, Q.license_number, R.region_description, A.people_id
from staff_view A
left join staff_site_link_expanded_view C on C.people_id = A.people_id
left join facility_view Q on Q.group_profile_id = C.group_profile_id
left join regions R on R.regions_id = Q.regions_id
WHERE C.STAFF_NAME IS NOT NULL
GROUP BY C.STAFF_NAME, C.job_title, C.id_number, C.billing_staff_credentials_code, C.site_name, C.group_profile_id, Q.license_number, R.region_description, A.people_id
ORDER BY C.STAFF_NAME
But I am wondering what is the purpose of the "Employee_Hierarchy"? When I replaced "staff_view" in the outer query with "Employee_Hierarchy", it only returned one record = "Kromer". So when/where can we use "Employee_Hierarchy"?
See:
SQL Server - Simple example of a recursive CTE
MSDN: Recursive Queries using Common Table Expression
SQL Server recursive CTE (this seems pretty much like exactly what you are working on!)
Update:
A proper recursive CTE consist of basically three things:
an anchor SELECT to begin with; that can select e.g. the root level employees (where the Reports_To is NULL), or it can select any arbitrary employee that you define, e.g. by a parameter
a UNION ALL
a recursive SELECT statement that selects from the same, typically self-referencing table and joins with the recursive CTE being currently built up
This gives you the ability to recursively build up a result set that you can then select from.
If you look at the Northwind sample database, it has a table called Employees which is self-referencing: Employees.ReportsTo --> Employees.EmployeeID defines who reports to whom.
Your CTE would look something like this:
;WITH RecursiveCTE AS
(
-- anchor query; get the CEO
SELECT EmployeeID, FirstName, LastName, Title, 1 AS 'Level', ReportsTo
FROM dbo.Employees
WHERE ReportsTo IS NULL
UNION ALL
-- recursive part; select next Employees that have ReportsTo -> cte.EmployeeID
SELECT
e.EmployeeID, e.FirstName, e.LastName, e.Title,
cte.Level + 1 AS 'Level', e.ReportsTo
FROM
dbo.Employees e
INNER JOIN
RecursiveCTE cte ON e.ReportsTo = cte.EmployeeID
)
SELECT *
FROM RecursiveCTE
ORDER BY Level, LastName
I don't know if you can translate your sample to a proper recursive CTE - but that's basically the gist of it: anchor query, UNION ALL, recursive query