The following query selects a students names and their highest score for a particular row. The problem is that the subquery in the left join can't be used.
I get the Teradata data error: "Object Date_View doesn't exist'". How can this be fixed?
Select name, max_score_today.max_score From Student_View
Left Join Date_view
ON Date_View.date=Student_View.date
Left Join (
Select MAX(score) as max_score FROM
Score_View
Where Date_View.start_date=Score_View.date
) max_score_today
ON max_score_today.name=Student_View.name
Move your correlated subquery up into the select statement, such as:
select name,
(select max(score) from score_view where date_view.start_date) = score_view.date) as max_score
from student_view
left join
date_view
on date_view.date = student_view.date;
To get the row with the highest/lowest value you better use RANK or ROW_NUMBER like this:
Select *
From Student_View
Left Join Date_view
on Date_View.date=Student_View.date
Left Join Score_View
on Date_View.start_date=Score_View.date
and Score_View.name=Student_View.name
QUALIFY -- get the highest score for each student/date
ROW_NUMBER() -- maybe RANK
OVER (PARTITION BY Student_View.name, Score_View.date
ORDER BY Score_View.score DESC) = 1
I'm not sure if this the correct result, you might have to change the PARTITION expression...
Related
SELECT
COUNT(follow."FK_accountId"),
score.*
FROM
(
SELECT items.*, AVG(reviews.score) as "averageScore" FROM "ITEM_VARIATION" as items
INNER JOIN "ITEM_REVIEW" as reviews ON reviews."FK_itemId"=items.id
GROUP BY items.id
) as score
INNER JOIN "ITEM_FOLLOWER" as follow ON score.id=follow."FK_itemId"
GROUP BY score.id
Inner Block works by itself and I believe I followed the same format.
However it outputs error:
ERROR: column "score.name" must appear in the GROUP BY clause or be used in an aggregate function
LINE 18: score.*
^
Is listing all the columns in score field only solution?
there are over 10 columns to list so I'd like to avoid that solution if it's not the only one
columns not included on the aggregation must be specified during group by
SELECT
COUNT(follow."FK_accountId"),
score.id,
score.name
FROM
(
SELECT items.id as id, items.name as name, AVG(reviews.score) as "averageScore" FROM "ITEM_VARIATION" as items
INNER JOIN "ITEM_REVIEW" as reviews ON reviews."FK_itemId"=items.id
GROUP BY items.id, items.name
) as score
INNER JOIN "ITEM_FOLLOWER" as follow ON score.id=follow."FK_itemId"
GROUP BY score.id, score.name
I would suggest you use correlated subqueries or a lateral join:
SELECT i.*,
(SELECT AVG(r.score)
FROM "ITEM_REVIEW" r
WHERE r."FK_itemId" = i.id
) as averageScore,
(SELECT COUNT(*)
FROM "ITEM_FOLLOWER" f
WHERE f."FK_itemId" = i.id
)
FROM "ITEM_VARIATION" i;
With the right indexes, this is probably faster as well.
I couldn't get this query working :
DOESN'T WORK
select
Region.*, count(secteur.*) count
from
Region
left join
secteur on secteur.region_id = Region.id
The solution I found is this but is there a better solution using joins or if this doesn't affect performance, because I have a very large dataset of about 500K rows
WORKS BUT AFRAID OF PERFORMANCE ISSUES
select
Region.*,
(select count(*)
from Secteur
where Secteur.Region_id = region.id) count
from
Region
I would suggest:
select region.*, count(secteur.region_id) as count
from region left join secteur on region.id = secteur.region_id
group by region.id, region.field2, region.field3....
Note that count(table.field) will ignore nulls, whereas count(*) will include them.
Alternatively, left join on a subquery and use coalesce to avoid nulls:
select region.*, coalesce(t.c, 0) as count
from region left join
(select region_id, count(*) as c from secteur group by region_id) t on region.id = t.region_id
I'd join region on an aggregate query of secteur:
SELECT r.*, COALESCE(s.cnt, 0)
FROM region r
LEFT JOIN (SELECT region_id, COUNT(*) AS cnt
FROM secteur
GROUP BY region_id) s ON s.region_id = r.id
I would go with this query:
select r.*,
(select count(*)
from Secteur s
where s.Region_id = r.id
) as num_secteurs
from Region r;
Then fix the performance problem by adding an index on Secteur(region_id):
create index idx_secteur_region on secteur(region_id);
You make a two mistakes
First: you have try to calulate COUNT() in only one (I mean, the second) table. This doesn't will work because theCOUNT(), like an any aggregate function, calculates only for the whole set of rows, not just for any part of the set (not only just for the one or an other joined table).
In your first query, you may replace secteur. * only by asterisk, like a Region.region_id, count(*) AS count, and do not forget add Region.region_id on the GROUP BY step.
Second: You has define not only aggregate function in the query, but and other fields: select Region.*, but you don't define them in GROUP BY step. You need to add to GROUP BY statement all columns, which you has define in the SELECT step but not apply an aggregate functions to them.
Append: not, GROUP BY Region.* doesn't will work, you should to define a columns in the GROUP BY step by their actual names.
So, correct form of this will looks like a
SELECT
Region.col1
,Region.col2,
, count(*) count
from Region
left join
secteur on secteur.region_id = Region.id
GROUP BY Region.col1, Region.col2
Or, if you don't want to type each name of column, use window queries
SELECT
Region.*,
, count( * ) OVER (PARTITION BY region_id) AS count
from Region
left join
secteur on secteur.region_id = Region.id
As mentioned in the title I want to display only row with maximum number, for this case it´s number 4 and nothing less.
select divak.MENO,count(divak.MENO)
from sledovanost
natural join tv_stanice
natural join divak
group by divak.meno
order by count(divak.MENO)desc;
My query
You can achieve this by a having-clause, in which you compare each MENO count with the maximum MENO count (retrieved by a subquery):
select divak.MENO,count(divak.MENO)
from sledovanost
natural join tv_stanice
natural join divak
group by divak.meno
having count(divak.MENO) = (
select (max(count(divak.MENO))
from sledovanost
natural join tv_stanice
natural join divak
group by divak.meno)
BTW: I'd change the query to join .. ON .. syntax; natural join, which connects tables on equally named attributes, bears the danger of "unintended connections" whenever the db schema changes.
Don't use natural join. It uses the names of the columns to match tables, and doesn't show the names in the query. It is a bug waiting to happen. Use USING or ON.
In Oracle, you would normally do this using row_number() or rank() depending on whether or not you wanted duplicates:
with t as (<your query here but name the second column>)
select t.*
from (select t.*, rank() over (order by cnt desc) as seqnum
from t
) t
where seqnum = 1;
Well, in order to get the last entry by date i've done that query :
select cle
from ( select cle, clepersonnel, datedebut, row_number()
over(partition by clepersonnel order by datedebut desc) as rn
from periodeoccupation) as T
where rn = 1
This one is working and give me the last entry by date, so far i'm ok.
But its the first time i work with subquery and i have to make my query way more complex with multiple joins. But i cannot figure out how to make a subquery in a inner join.
This is what i try :
select personnel.prenom, personnel.nom
from personnel
inner join
( select cle, clepersonnel, datedebut, row_number()
over(partition by clepersonnel order by datedebut desc) as rn
from periodeoccupation) as T
ON personnel.cle = periodeoccupation.clepersonnel
where rn = 1
but its not working !
If you have any idea or tips...Thank you !
Simply change
ON personnel.cle = periodeoccupation.clepersonnel
to
ON personnel.cle = T.clepersonnel
The query join has been aliased with T and you have reference the alias as the table in the aliased query is out of scope in your outer statement.
select
picks.`fbid`,
picks.`time`,
categories.`name` as cname,
options.`name` as oname,
users.`name`
from
picks
left join categories
on (categories.`id` = picks.`cid`)
left join options
on (options.`id` = picks.oid)
left join users
on (users.fbid = picks.`fbid`)
order by
time desc
that query returns a result that like:
my question is.... I would like to modify the query to select only DISTINCT fbid's. (perhaps the first row only sorted by time)
can someone help with this?
select
p2.fbid,
p2.time,
c.`name` as cname,
o.`name` as oname,
u.`name`
from
( select p1.fbid,
min( p1.time ) FirstTimePerID
from picks p1
group by p1.fbid ) as FirstPerID
JOIN Picks p2
on FirstPerID.fbid = p2.fbid
AND FirstPerID.FirstTimePerID = p2.time
LEFT JOIN Categories c
on p2.cid = c.id
LEFT JOIN Options o
on p2.oid = o.id
LEFT JOIN Users u
on p2.fbid = u.fbid
order by
time desc
I don't know why you originally had LEFT JOINs, as it appears that all picks must be associated with a valid category, option and user... I would then remove the left, and change them to INNER joins instead.
The first inner query grabs for each fbid, the FIRST entry time which will result in a single entity for the FBID. From that, it re-joins to the picks table for the same ID and timeslot... then continues for the rest of the category, options, users join criteria of that single entry.
2 options, you could write a group by clause.
Or you could write a nested query joined back to itself to get pertinent info.
Nested aliased table:
SELECT
n.fBids
FROM
MyTable t
INNER JOIN
(SELECT DISTINCT fBids
FROM MyTable) n
ON n.ID = t.ID
Or group by option
SELECT fBId from MyTable
GROUP BY fBID
select picks.`fbid`, picks.`time`, categories.`name` as cname,
options.`name` as oname, users.`name` from picks left join categories
on (categories.`id` = picks.`cid`) left join options on (options.`id` = picks.oid)
left join users on (users.fbid = picks.`fbid`)
order by time desc GROUP BY picks.`fbid`
select
picks.fbid,
MIN(picks.time) as first_time,
MAX(picks.time) as last_time
from
picks
group by
picks.fbid
order by
MIN(picks.time) desc
However, if you want only distinct fbid's you cannot display cname and other columns at the same time.