I have a big query, but it all boils down to this:
SELECT * FROM user
LEFT JOIN tableA ON tableA.user_id = user.id
JOIN tableB ON tableB.a_id = tableA.id
Now, I get too few results. If the combination of user with (tableA x tableB) does not exist, I still want the user. So with syntax error, what I want is something like this:
SELECT * FROM user
LEFT JOIN (tableA ON tableA.user_id = user.id
JOIN tableB ON tableB.a_id = tableA.id)
is that possible, perhaps without RIGHT JOINS?
Of course, I don't want to change the second JOIN to LEFT JOIN, because that would give too many results.
You can try this:
SELECT * FROM user
LEFT JOIN (SELECT * FROM tableA
JOIN tableB ON tableB.a_id = tableA.id) t
ON t.user_id = user.id
You will need to select distinct columns in subquery here if any exists.
Related
I'm relatively new to derived tables when querying in From/Join clause as I always thought that Joins would eliminate the need for these subqueries. However, my question is that when I write a subquery within an inner join, do I need to specify the Joining column field within the subquery select statement to initiate a Join? I know you don't usually have to do this in a normal Join, however I wrote some sql code that won't execute unless I specify the joining column in the subquery select statement (I've bolded this). I've pasted the code below.
select pc.category_name
,product_name
,pp.list_price
,avg(quantity * (oi.list_price * (1-discount))) as Average_Revenue
,sum(quantity) as [products sold]
,sum(quantity * (oi.list_price * (1-discount))) as Revenue
,dt.Average_Category_Revenue
from production.categories as pc
inner join production.products as pp
on pc.category_id = pp.category_id
inner join sales.order_items as oi
on pp.product_id = oi.product_id
inner join (
select
category_name
,**pcc.category_id**
,avg(quantity * (oii.list_price * (1-discount))) as Average_Category_Revenue
from production.categories as pcc
inner join production.products as ppp
on pcc.category_id = ppp.category_id
inner join sales.order_items as oii
on ppp.product_id = oii.product_id
group by category_name, pcc.category_id
) as dt
on pp.category_id = dt.category_id
group by pc.category_name, product_name, pp.list_price, dt.Average_Category_Revenue
order by sum(quantity * (oi.list_price * (1-discount))) DESC
I have a query similar to this simplified example:
select u.id, sq.score
from usr as u,
(select user_id, score FROM score WHERE bar = ?) as sq
where u.id = sq.user_id
I would like the join (u.id = sq.user_id) to be an outer join. I can't figure out how to use JOIN in the from clause with a 'select' like this.
I know I could do this example without having to use a select in the from clause but thats not what I need in my application.
Something like this:
select u.id, sq.score
from usr as u
left join ( -- or right/full join as per your needs
select user_id, score FROM score WHERE bar = ?
) as sq
on u.id = sq.user_id
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.
I have a stored procedure which is running quite slow. Therefore I want to extract some of the query in a separate view.
My code looks something like this:
DECLARE #tmpTable TABLE(..)
INSERT INTO #tmpTable (..) *query* (returns 3000 rows)
Select ... from table1
inner join table2
inner join table3
inner join #tmpTable
...
I then extract (copy-paste) the *query* and put it in a view - i.e. vView.
Doing this will then give me a different result:
Select ... from table1
inner join table2
inner join table3
inner join vView
...
Why? I can see that the vView and the #tmpTable both returns 3000 rows, so they should match (also did a except query to check).
Any comments would be much appriciated as I feel quite stuck with this..
EDITED:
This is the full query for getting the result (using #tmpTable or vView gives me different results, although the appear the same):
select dep.sid as depsid, dep.[name], COUNT(b.sid) as possiblelogins, count(ls.clientsid) as logins
from department dep
inner join relationship r on dep.sid=r.primarysid and r.relationshiptypeid=27 and r.validto is null
inner join [user] u on r.secondarysid=u.sid
inner join relationship r2 on u.sid=r2.secondarysid and r2.validto is null and r2.relationshiptypeid in (1,37)
inner join client c on r2.primarysid=c.sid
inner join ***#tmpTable or vView*** b on b.sid = c.sid
left outer join (select distinct clientsid from logonstatistics) as ls on b.sid=ls.clientsid
GROUP BY dep.sid, dep.[name],dep.isdepartment
HAVING dep.isdepartment=1
You maybe don't need the view/table if you change to this.
It joins on to client c and appears to be there only to JOIN onto logonstatistics
--remove inner join ***#tmpTable or vView*** b on b.sid = c.sid
--change JOIN
left outer join (select distinct clientsid from logonstatistics) as ls on c.sid=ls.clientsid
And change COUNT(b.sid) to COUNT(c.sid) in the SELECT clause
Otherwise, if you get different results you have two options I can see:
Table and view have different data. Have you run a line by line comparsion?
One has NULL, one has a value (especially for the sid column which will affect the JOIN)
Finally, when you says "different results" do you mean you get x2 or x3 rows? A different COUNT? What?