SELECT course_categories.course_category_title, COUNT(*) as count
FROM course_enrollments
JOIN courses ON course_enrollments.course_id = courses.course_id
JOIN course_categories ON course_categories.id = courses.course_category_id"
GROUP BY course_categores.id
ORDER BY courses_categories.title
How would I do this in rails: (I tried the below with major errors)
category_rs = CourseEnrollment.select("course_categories.title, COUNT(*) as count").
joins(:courses, :course_categories).
group("course_categories.id").
order("course_categories.title")
I figured it out, I needed to specify the join as a string.
Related
created a view called winners, it contains the columns: athlete_name,year,medal_won
its basicly athletes that won olympic medal and the year,
it look like that,
data base is in live sql: https://livesql.oracle.com/apex/f?p=590:1000:0
select distinct year,athlete_name,medal
from olym.olym_medals
join olym.olym_athlete_games on olym_athlete_games.id = olym_medals.athlete_game_id
join olym.olym_nations on olym_nations.id = olym_athlete_games.nation_id
join olym.olym_games on olym_games.id = Olym_athlete_games.game_id
join olym.olym_athletes on olym_athletes.id = olym_athlete_games.athlete_id
order by athlete_name
as you can see some name show only once and some names are showing more than once, i want to get rid off all lines of those who show ONLY ONCE, please help me.
thank you!
if i have understand your problem, must group your data,
select year,athlete_name,medal, count(*) "number of Medals"
from olym.olym_medals
join olym.olym_athlete_games on olym_athlete_games.id = olym_medals.athlete_game_id
join olym.olym_nations on olym_nations.id = olym_athlete_games.nation_id
join olym.olym_games on olym_games.id = Olym_athlete_games.game_id
join olym.olym_athletes on olym_athletes.id = olym_athlete_games.athlete_id
group by year,athlete_name,medal;
If I followed you correctly, you can use window functions:
select *
from (
select og.year, oa.athlete_name, om.medal, count(*) over(partition by oa.id) cnt
from olym.olym_medals om
join olym.olym_athlete_games oag on oag.id = om.athlete_game_id
join olym.olym_nations ona on ona.id = oag.nation_id
join olym.olym_games og on og.id = oag.game_id
join olym.olym_athletes oa on oa.id = oag.athlete_id
) t
where cnt > 1
order by athlete_name
Notes:
I am unsure why you were using distinct in the first place, so I removed it (I suspect it is actually not needed)
I added table aliases to shorten the query, and prefixed the columns in the select clause with the table they belong to (you might want to review that) - these are best practices when dealing with multi-table queries
Use GROUP BY and HAVING COUNT(*) > 1:
SELECT year,
athlete_name,
medal
FROM olym.olym_medals
INNER JOIN olym.olym_athlete_games
ON olym_athlete_games.id = olym_medals.athlete_game_id
INNER JOIN olym.olym_nations
ON olym_nations.id = olym_athlete_games.nation_id
INNER JOIN olym.olym_games
ON olym_games.id = Olym_athlete_games.game_id
INNER JOIN olym.olym_athletes
ON olym_athletes.id = olym_athlete_games.athlete_id
GROUP BY
year,
athlete_name,
medal
HAVING COUNT(*) > 1
ORDER BY athlete_name
Table with orders has another table with positions. I want the orders table to show but then only have the most up to-date position on it. Below is a picture of the 3 rows I want showing. Omit the rest.
SELECT DispatchTable.ordernumber, DispatchTable.truck,
DispatchTable.driver, DispatchTable.actualpickup,
DispatchTable.actualdropoff, orders.pickupdateandtime,
orders.dropoffdateandtime, Truck002.lastposition,
Truck002.lastdateandtime
FROM DispatchTable
INNER JOIN orders ON DispatchTable.ordernumber = orders.id
INNER JOIN Truck002 ON DispatchTable.truck = Truck002.name
WHERE (orders.status = 'onRoute')
Assuming that you want the row having the latest lastdateandtime for the truck name, this should work:
SELECT DispatchTable.ordernumber,
DispatchTable.truck,
DispatchTable.driver,
DispatchTable.actualpickup,
DispatchTable.actualdropoff,
orders.pickupdateandtime,
orders.dropoffdateandtime,
TruckLatest.lastposition,
TruckLatest.lastdateandtime
FROM DispatchTable
INNER JOIN orders ON DispatchTable.ordernumber = orders.id
INNER JOIN (SELECT name,
lastposition,
lastdateandtime
FROM Truck002 Truck1
WHERE lastdateandtime =
(SELECT MAX(lastdateandtime)
FROM Truck002 Truck2
WHERE Truck2.name = Truck1.name)) TruckLatest
ON DispatchTable.truck = TruckLatest.name
WHERE (orders.status = 'onRoute')
If I understand correctly, you can get the most recent record for a truck using ROW_NUMBER():
SELECT dt.ordernumber, dt.truck,
dt.driver, dt.actualpickup,
dt.actualdropoff, o.pickupdateandtime,
o.dropoffdateandtime, t.lastposition,
t.lastdateandtime
FROM DispatchTable dt INNER JOIN
orders o
ON dt.ordernumber = o.id INNER JOIN
(SELECT t.*,
ROW_NUMBER() OVER (PARTITION BY t.name ORDER BY t.lastdateandtime DESC) as seqnum
FROM Truck002 t
) t
ON dt.truck = t.name
WHERE o.status = 'onRoute' AND seqnum = 1;
Firstly, why are you using Truck002's name field rather than its id field as the link to DispacthTable? This is considered a less efficient way of doing it than using id (which is either a numerical field or a shorter string than name).
Secondly, you should mention in your Question that each Order can have many DispatchTable's and that each DispacthTable can have many Truck002's, otherwise many people will start by assuming that it is the other way round between DispatchTable and Truck002.
Thirdly, please try...
SELECT DispatchTable.ordernumber,
DispatchTable.truck,
DispatchTable.driver,
DispatchTable.actualpickup,
DispatchTable.actualdropoff,
orders.pickupdateandtime,
orders.dropoffdateandtime,
Truck002.lastposition,
Truck002.lastdateandtime
FROM DispatchTable
INNER JOIN orders ON DispatchTable.ordernumber = orders.id
INNER JOIN Truck002 ON DispatchTable.truck = Truck002.name
WHERE (orders.status = 'onRoute')
GROUP BY ordernumber
HAVING lastdateandtime = MAX( lastdateandtime )
If you have any questions or comments, then please feel free to post a Comment accordingly.
Further Reading
https://msdn.microsoft.com/en-us/library/bb177906(v=office.12).aspx (on HAVING)
https://www.w3schools.com/sql/sql_having.asp (on HAVING)
https://msdn.microsoft.com/en-us/library/bb177905(v=office.12).aspx (on GROUP BY)
https://www.w3schools.com/sql/sql_groupby.asp (on GROUP BY)
I have the query below working, the thing is I need to only list each unique "VolumeSerialNumber0" once. There's no shortage of questions and approaches to this problem on SO but they suggest using subqueries and group by clause, but when I try to do that I get an error "columnname is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.
I feel like it has to be close I'm just not getting the magical syntax perfectly correct.
SELECT
dbo.v_R_System.Netbios_Name0,
dbo.v_GS_LOGICAL_DISK.TimeStamp,
dbo.v_GS_LOGICAL_DISK.Description0,
dbo.v_GS_LOGICAL_DISK.DeviceID0,
dbo.v_GS_LOGICAL_DISK.DriveType0,
dbo.v_GS_LOGICAL_DISK.Name0,
dbo.v_GS_LOGICAL_DISK.SystemName0,
dbo.v_GS_LOGICAL_DISK.VolumeName0,
dbo.v_GS_LOGICAL_DISK.VolumeSerialNumber0,
dbo.v_GS_PARTITION.Size0,
dbo.v_GS_LOGICAL_DISK.FileSystem0
FROM
dbo.v_R_System
INNER JOIN dbo.v_GS_LOGICAL_DISK
ON dbo.v_R_System.ResourceID = dbo.v_GS_LOGICAL_DISK.ResourceID
INNER JOIN dbo.v_GS_PARTITION
ON dbo.v_GS_LOGICAL_DISK.ResourceID = dbo.v_GS_PARTITION.ResourceID
SELECT
MAX(S.Netbios_Name0),
MAX(L.TimeStamp),
MAX(L.Description0),
MAX(L.DeviceID0),
MAX(L.DriveType0),
MAX(L.Name0),
MAX(L.SystemName0),
MAX(L.VolumeName0),
L.VolumeSerialNumber0,
MAX(P.Size0),
MAX(L.FileSystem0)
FROM
dbo.v_R_System S
INNER JOIN dbo.v_GS_LOGICAL_DISK L
ON S.ResourceID = L.ResourceID
INNER JOIN dbo.v_GS_PARTITION P
ON L.ResourceID = P.ResourceID
GROUP BY
L.VolumeSerialNumber0
I have this strange error in SQL Server 2005 where I take a working query, add the UNION keyword below it and then copy the query again. In my opinion, this should always be working, but it is not. I get the message 'Incorrect syntax near the keyword 'union'.
What could create this problem ?
To be more specific, here is the complete query :
select distinct deliveries.id, orders.id, 20 + sum(orders.mass1) as allowed_duration
from features_resources
inner join features on features.id = featureid
inner join orders on orders.id = features_resources.resourceid
inner join orderinformations on orders.id = orderinformations.orderid
inner join deliveries on orderinformations.deliveryid = deliveries.id
where features.name = 'O_FRAIS'
and (deliveries.ID IN
(SELECT ID
FROM dbo.DeliveriesInExportedSchedule))
group by deliveries.id, features.name ,orders.id order by deliveries.id
union
select distinct deliveries.id, orders.id, 20 + sum(orders.mass1) as allowed_duration
from features_resources
inner join features on features.id = featureid
inner join orders on orders.id = features_resources.resourceid
inner join orderinformations on orders.id = orderinformations.orderid
inner join deliveries on orderinformations.deliveryid = deliveries.id
where features.name = 'O_FRAIS'
and (deliveries.ID IN
(SELECT ID
FROM dbo.DeliveriesInExportedSchedule))
group by deliveries.id, features.name ,orders.id order by deliveries.id
I have tried to reproduce the error on a smaller query, by starting from a simple query and adding features one by one (inner join, nested queryes, group by, sum,....) but failed to reproduce the error again.
Any idea ?
It is actually the order by deliveries.id in the top half that causes the problem.
The order by needs to apply to the whole query.
Example Syntax
SELECT v1.number
FROM master.dbo.spt_values v1
WHERE v1.number > 2000
UNION
SELECT v2.number
FROM master.dbo.spt_values v2
WHERE v2.number < 10
ORDER BY v1.number
Try putting the individual SELECTs in parentheses:
(SELECT ... )
UNION
(SELECT ... )
The way you have it now, the second WHERE and GROUP BY clauses are ambiguous - should that apply to the SELECT, or to the UNION? I don't have any way to tell, and neither has your DB server.
Alright, so I'm putting together a path to select a revision of a particular novel:
SELECT Catalog.WbsId, Catalog.Revision, NovelRevision.Revision
FROM Catalog, BookInCatalog
INNER JOIN NovelMaster
INNER JOIN HasNovelRevision
INNER JOIN NovelRevision
ON HasNovelRevision.right = NovelRevision.obid
ON HasNovelRevision.Left=NovelMaster.obid
ON NovelMaster.obid = BookInCatalog.Right
WHERE Catalog.obid = BookInCatalog.Left;
This returns all revisions that are in the Novel Master for each Novel Master that is in the catalog.
The problem is, I only want the FIRST revision of each novel master in the catalog. How do I go about doing that? Oh, and btw: my flavor of sql is hobbled, as many others are, in that it does not support the LIMIT Function.
****UPDATE****
So using answer 1 as a guide I upgraded my query to this:
SELECT Catalog.wbsid
FROM Catalog, BookInCatalog, NovelVersion old, NovelMaster, HasNovelRevision
LEFT JOIN NovelVersion newRevs
ON old.revision < newRevs.revision AND HasNovelRevision.right = newRevs.obid
LEFT JOIN HasNovelRevision NewerHasNovelRevision
ON NewerHasNovelRevision.right = newRevs.obid
LEFT JOIN NovelMaster NewTecMst
ON NewerHasNovelRevision.left = NewTecMst.obid
WHERE Catalog.programName = 'E18' AND Catalog.obid = BookInCatalog.Left
AND BookInCatalog.right = NewTecMst.obid AND newRevs.obid = null
ORDER BY newRevs.documentname;
I get an error on the fourth line:
"old"."revision": invalid identifier
SOLUTION
Well, I had to go to another forum, but I got a working solution:
select nr1.title, nr1.revision
from novelrevision nr1
where nr1.revision in (select min(revision) from novelrevision nr2
where nr1.title = nr2.title)
So this solution uses the JOIN mentioned by the OA, along with the IN keyword to match it to a revision.
Something like this might work, it's called an exclusive left join:
....
INNER JOIN NovelRevision
ON HasNovelRevision.right = NovelRevision.obid
LEFT JOIN NovelRevision as NewerRevision
ON HasNovelRevision.right = NewerRevision.obid
AND NewerRevision.revision > NovelRevision.revision
...
WHERE NeverRevision.obid is null
The where clause filters out rows for which a newer revision exists. This effectively limits the query to the newest revisions.
In response to your comment, you could filter out only revisions that have a newer revision in the same NovelMaster. For example:
....
LEFT JOIN NovelRevision as NewerRevision
ON HasNovelRevision.right = NewerRevision.obid
AND NewerRevision.revision > NovelRevision.revision
LEFT JOIN HasNovelRevision as NewerHasNovelRevision
ON NewerHasNovelRevision.right = NewerRevision.obid
LEFT JOIN NovelMaster as NewerNovelMaster
ON NewerHasNovelRevision.left = NewerNovelMaster.obid
AND NewerNovelMaster.obid = NovelMaster.obid
....
WHERE NeverNovelMaster.obid is null
P.S. I don't think you can group JOINs and follow them with a group of ON conditions. An ON must directly follow its JOIN.
You can use CTE
Check this
WITH NovelRevesion_CTE(obid,RevisionDate)
AS
(
SELECT obid,MIN(RevisionDate) RevisionDate FROM NovelRevision Group by obid
)
SELECT Catalog.WbsId, Catalog.Revision, NovelRevision.Revision
FROM Catalog, BookInCatalog
INNER JOIN NovelMaster
INNER JOIN HasNovelRevision
INNER JOIN NovelRevesion
INNER JOIN NovelRevesion_CTE
ON HasNovelRevision.[right] = NovelRevision.obid
ON HasNovelRevision.[Left]=NovelMaster.obid
ON NovelMaster.obid = BookInCatalog.[Right]
ON NovelRevesion_CTE.obid = NovelRevesion.obid
WHERE Catalog.obid = BookInCatalog.[Left];
First it select the first revision written for each novel (assuming obid is novel foriegn key) by taking the smallest date and group them.
then add it as join in your query