I have the following SQL query that performs horribly due to the select count(1) statement in the where clause. Can anyone suggest a way that would speed this up? The idea is that I only want rows returned where there is one invoice found.
SELECT people.name, people.address
FROM people
WHERE ((SELECT COUNT(1) FROM invoices WHERE invoices.pid = people.id)=1)
COUNT(1) is superstition
What you have is a count per row of people = a cursor/loop like action
So, try a JOIN like this
SELECT people.name, people.address
FROM
people
JOIN
invoices ON invoices.pid = people.id
GROUP BY
people.name, people.address
HAVING
COUNT(*) = 1
I'd also hope you have indexes, at least on invoices.pid and people.pid, name, address
Use a JOIN:
SELECT people.name, people.address
FROM people
JOIN invoices ON invoices.pid = people.id
GROUP BY people.name, people.address
HAVING Count(*) = 1
Joining the tables is probably going to be much better in practice and in performance, I should think.
SELECT people.name, people.address
FROM people INNER JOIN invoices ON invoices.pid = people.id
Edit due to OP being edited: do you want only those people who have exactly one invoice? If so then disregard this and look at one of the other answers.
Related
I am struggling with taking a Count() from one table and dividing it by a correlating number from a different table in Microsoft SQL Server.
Here is a fictional example of what I'm trying to do
Lets say I have a table of orders. One column in there is states.
I have a second table that has a column for states, and second column for each states population.
I'd like to find the order per population for each sate, but I have struggled to get my query right.
Here is what I have so far:
SELECT Orders.State, Count(*)/
(SELECT StatePopulations.Population FROM Orders INNER JOIN StatePopulations
on Orders.State = StatePopulations.State
WHERE Orders.state = StatePopulations.State )
FROM Orders INNER JOIN StatePopulations
ON Orders.state = StatePopulations.State
GROUP BY Orders.state
So far I'm contending with an error that says my sub query is returning multiple results for each state, but I'm newer to SQL and don't know how to overcome it.
If you really want a correlated sub-query, then this should do it...
(You don't need to join both table in either the inner or outer query, the correlation in the inner query's where clause does the 'join'.)
SELECT
Orders.state,
COUNT(*) / (SELECT population FROM StatePopulation WHERE state = Orders.state)
FROM
Orders
GROUP BY
Orders.state
Personally, I'd just join them and use MAX()...
SELECT
Orders.state,
COUNT(*) / MAX(StatePopulation.population)
FROM
Orders
INNER JOIN
StatePopulation
StatePopulation.state = Orders.state
GROUP BY
Orders.state
Or aggregate your orders before you join...
SELECT
Orders.state,
Orders.order_count / StatePopulation.population
FROM
(
SELECT
Orders.state,
COUNT(*) AS order_count
FROM
Orders
GROUP BY
Orders.state
)
Orders
INNER JOIN
StatePopulation
StatePopulation.state = Orders.state
(Please forgive typos and smelling pistakes, I'm doing this on a phone.)
I am in need of a very strange problem. I hope you brilliant guys will enjoy this problem (or may be it's an easy task for you :) ).
Here is the query I am using to return values from three tables
select listing.*
, sum(review.rNumber) as nor
, count(review.rNumber) as total
, users.username from listing
where
left join review on listing.lid=review.lID
inner join users on users.uid=listing.cuid
group by listing.lid
Now in this query I want to use an additional filter. It is returning all the values from listing table but I want to return all values using WHERE cat='Hair' or something
I don't have any idea how to insert where clues in this query.. Please let me know if it doable.
Thanks
If you want the filter to apply before the group by:
select listing.*, sum(review.rNumber) as nor, count(review.rNumber) as total, users.username from listing
left join review on listing.lid=review.lID
inner join users on users.uid=listing.cuid
where cat='Hair'
group by listing.lid
If you want it after, you use "having" instead:
select listing.*, sum(review.rNumber) as nor, count(review.rNumber) as total, users.username from listing
left join review on listing.lid=review.lID
inner join users on users.uid=listing.cuid
group by listing.lid
having cat='Hair'
Your query should be as follow.
select listing.lid
, sum(review.rNumber) as nor
, count(review.rNumber) as total
, users.username from listing
left join review on listing.lid=review.lID
inner join users on users.uid=listing.cuid
where
cat='Hair
group by listing.lid,users.username
First of all, you need to follow
Select
From
Where
Group By
Second, if you use group by, you may not select any column that is not in aggregate function or in group by. Therefore, listing.* can not be done. If you need that values, put them in the both group by and select.
I'm new to SQL and I'm currently trying to learn how to make reports in Visual Studio. I need to make a table, graph and few other things. I decided to do matrix as the last part and now I'm stuck. I write my queries in SQL Server.
I have two tables: Staff (empID, StaffLevel, Surname) and WorkOfArt (artID, name, curator, helpingCurator). In the columns Curator and HelpingCurator I used numbers from empID.
I'd like my matrix to show every empID and the number of paintings where they're acting as a Curator and the number of paintings where they're acting as a Helping Curator (so I want three columns: empID, count(curator), count(helpingCurator).
Select Staff.empID, count(WorkOfArt.Curator) as CuratorTotal
FROM Staff, WorkOfArt
WHERE Staff.empID=WorkOfArt.Curator
and Staff.StaffLevel<7
group by Staff.empID;
Select Staff.empID, count(WorkOfArt.HelpingCurator) as HelpingCuratorTotal
FROM Staff, WorkOfArt
WHERE Staff.empID=WorkOfArt.HelpingCurator
and Staff.StaffLevel<7
group by Staff.empID;
I created those two queries and they work perfectly fine, but I need it in one query.
I tried:
Select Staff.empID, count(WorkOfArt.Curator) as CuratorTotal,
COUNT(WorkOfArt.HelpingCurator) as HelpingCuratorTotal
FROM Staff FULL OUTER JOIN WorkOfArt on Staff.empID=WorkOfArt.Curator
and Staff.empID=WorkOfArt.HelpingCurator
WHERE Staff.StaffLevel<7
group by Staff.empID;
(as well as using left or right outer join)
- this one gives me a table with empID, but in both count columns there are only 0s - and:
Select Staff.empID, count(WorkOfArt.Curator) as CuratorTotal,
COUNT(WorkOfArt.HelpingCurator) as HelpingCuratorTotal
FROM Staff, WorkOfArt
WHERE Staff.empID=WorkOfArt.Curator
and Staff.empID=WorkOfArt.HelpingCurator
and Staff.StaffLevel<7
group by Staff.empID;
And this one gives me just the names of the columns.
I have no idea what to do next. I tried to find the answer in google, but all explanations I found were far more advanced for me, so I couldn't understand them... Could you please help me? Hints are fine as well.
The easiest way to do this is most likely with inner select in the select clause, with something like this:
Select
S.empID,
(select count(*) from WorkOfArt C where C.Curator = S.empID)
as CuratorTotal,
(select count(*) from WorkOfArt H where H.HelpingCurator = S.empID)
as HelpingCuratorTotal
FROM Staff S
WHERE S.StaffLevel<7
group by S.empID;
This way the rows with different role aren't causing problems with the calculation. If the tables are really large or you have a lot of different roles, then most likely more complex query with grouping the items first in the WorkOfArt table might have better performance since this requires reading the rows twice.
From a performance perspective, the following query is probably a little more efficient
select e.EmpId, CuratorForCount, HelpingCuratorForCount
from Staff s
inner join ( select Curator, count(*) as CuratorForCount
from WorkOfArt
group by Curator) mainCurator on s.EmpId = mainCurator.Curator
inner join ( select HelpingCurator, count(*) as HelpingCuratorForCount
from WorkOfArt
group by HelpingCurator) secondaryCurator on s.EmpId = secondaryCurator.HelpingCurator
One method, that can be useful if you want to get more than one value aggregated value from the WorkOfArt table is to pre-aggregate the results:
Select s.empID, COALESCE(woac.cnt, 0) as CuratorTotal,
COALESCE(woahc.cnt) as HelpingCuratorTotal
FROM Staff s LEFT JOIN
(SELECT woa.Curator, COUNT(*) as cnt
FROM WorkOfArt woa
GROUP BY woa.Curator
) woac
ON s.empID = woac.Curator LEFT JOIN
(SELECT woa.HelpingCurator, COUNT(*) as cnt
FROM WorkOfArt woa
GROUP BY woa.HelpingCurator
) woahc
ON s.empID = woahc.HelpingCurator
WHERE s.StaffLevel < 7;
Notice that the aggregation on the outer level is not needed.
I have two tables, People, and Vehicles. Vehicles belongs to people. Im trying to check if a person does not have a vehicle. I was attempting to do this by joining People and Vehicles, and displaying the persons ID that is NOT IN Vehicles.person_id.
This is returning nothing, and has me wondering if there is something I did wrong, or if there is a more efficient way of doing this.
Query is below
Select People.id
From People
INNER JOIN Vehicles
on People.id=Vehicles.person_id
where People.id NOT IN Vehicles.person_id;
Use left join to figure out the persons with no vehicles
Select distinct People.id
From People
LEFT JOIN Vehicles on People.id=Vehicles.person_id
where Vehicles.person_id is NULL
NOT IN can have issues with NULL values, and should probably be avoided for performance reasons if the subquery is very large.
Try NOT EXISTS:
SELECT p.id
FROM People p
WHERE NOT EXISTS (
SELECT 1
FROM Vehicles v
WHERE v.person_id = p.id)
another solution, using sets:
Select id From People
except
SELECT person_id FROM Vehicles
Use Subquery as below:
Select id
From People
WHERE id NOT IN (SELECT distinct person_id
FROM Vehicles
WHERE person_id IS NOT NULL)
select all people who are not in (by Select id From People WHERE id NOT IN) the List of all the people who has vehicle by SELECT distinct person_id FROM Vehicles (you could avoid null as well here if you want).
I'm trying to count authors who don't have any articles in our system, which aggregates authorship across sites. I've got a query working, but it isn't performant.
The best query I have thus far is this:
select count(*) as count_all
from (
select authors.id
from authors
left outer join site_authors on site_authors.author_id = authors.id
left outer join articles on articles.site_author_id = site_authors.id
group by authors.id
having count(articles.id) = 0
) a;
However, the subquery is rather inefficient. I was hoping there's a way to flatten this. I have several similar queries that add extra conditions on the left outer joins, so adding a count column to my schema isn't really an option here.
Extra rub: this is a cross-platform query and needs to work against both pgSQL, SQLite, and MySQL.
you can try a little bit different query, but I'm not sure that it will be faster:
select count(*)
from authors as a
where not exists (
select b.id
from site_authors as b
inner join
articles as c
on a.id=b.author_id and b.id=c.site_author_id)
of course I suppose you have proper indexes on tables:
site_authors: unique (author_id, id)
articles: non unique (site_author_id)
Assuming that 'normal' joins are simpler and faster, you could subtract the number of authors with articles from the total number of authors:
SELECT (SELECT COUNT(*)
FROM authors) -
(SELECT COUNT(DISTINCT site_authors.author_id)
FROM site_authors
JOIN articles ON articles.site_author_id = site_authors.id)
Alternatively, try a subquery:
SELECT COUNT(*)
FROM authors
WHERE id NOT IN (SELECT site_authors.author_id
FROM site_authors
JOIN articles ON articles.site_author_id = site_authors.id)
It might be simpler and faster to use NOT IN rather than a join. Sql processors are pretty smart about using indexes even when it looks obtuse. Something like this:
Select count(*)
from authors
where id not in (select author_id from site_authors)
and id not in (select site_author_id from articles);
Be sure that author_id and site_author_id are indexed. The optimizer will notice what your are doing and create an indexed look up for the "NOT IN" clause.