i have 2 tables gallery(Gallery_ID,Name) and Gallery_Image(ID,Gallery_ID,Image). My question is i want to select only one image of each gallery
i have tried this query
SELECT distinct top 1 Gallery.Gallery_ID, Gallery.Gallery_Name,Gallery.Gallery_Name as Gallery_Image
FROM Gallery
union
select distinct Gallery_Image.Gallery_ID,Gallery_Image.Gallery_Images as Gallery_Name,Gallery_Image.Gallery_Images
from Gallery_Image inner join Gallery on Gallery.Gallery_ID=Gallery_Image.Gallery_ID
where Gallery_Image.Gallery_ID in(select Gallery_ID from Gallery)
You say: "i want to select only one image of each gallery." This makes sense. I have no idea how your query relates to this question.
You don't specify which database you are using. A good approach is to use row_number() to assign a sequential order to the images within a gallery. The key is to do a random sort. The last piece depends on the database. Here is the SQL Server syntax:
select gi.*
from (select gi.*, row_number() over (partition by Gallery_Id order by newid()) as seqnum
from Gallery_Image gi
) gi
where seqnum = 1;
EDIT:
To get information from the Gallery table, join it in:
select gi.*
from (select gi.*, row_number() over (partition by Gallery_Id order by newid()) as seqnum
from Gallery_Image gi
) gi join
Gallery g
on gi.Gallery_Id = g.Gallery_Id and
seqnum = 1;
I also moved the logic to take the "first" image to the on clause from the where clause.
Related
I have the tables listed in the image. I need to display the institution and loan type of the most used financing plan in the sale_financing table. I have tried using the stats_mode function but I have not been able to get it to work. I am supposed to only display the most used financing plan and I keep getting 3 showing up. Here is an image of the tables.
My image may not work so here are the tables:
financing_plan
id
institution
loan_type
sale_financings
id
plan_id ------> foreign key linking to - financing_plan.id
I have tried several different ways in the Query Builder and I cannot get it to work.
Here is one :
SELECT
financing_plans.institution,
financing_plans.loan_type,
STATS_MODE(sale_financings.plan_id) AS stats_mode_plan_id
FROM
financing_plans
INNER JOIN sale_financings ON financing_plans.id =
sale_financings.plan_id
GROUP BY
financing_plans.institution,
financing_plans.loan_type
Another:
SELECT
financing_plans.institution,
financing_plans.loan_type,
STATS_MODE(sale_financings.plan_id) AS stats_mode_plan_id
FROM
financing_plans
INNER JOIN sale_financings ON financing_plans.id =
sale_financings.plan_id
GROUP BY
financing_plans.institution,
financing_plans.loan_type
HAVING
STATS_MODE(sale_financings.plan_id) = sale_financings.plan_id
Count the use of each plan_id, then rank these (using dense_rank()) by the count (descending order) allows "top" and "equal top" to be shown.
select
fp.institution, fp.loan_type, s.plan_count
from financing_plan fp
inner join (
select plan_id, plan_count, dense_rank() over(order by plan_count DESC) as rnk
from (
select plan_id, count(id) plan_count
from sale_financings
Group by plan_id
)
) s on fp.id = s.plan_id and s.rnk = 1
order by
fp.institution, fp.loan_type
;
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.
My Database has 3 Tables, Device,Postal_Address and Company.
Every Device has an Company_ID, and for every company there is an address. The problem is, the old address is still there if i change it, its everytime making a new entry for this. So if i select all devices with address i get some entrys doubled.
select d.device,
(
select postalcode_address from
(
select
pa.postalcode_address,
row_number() over (order by pa.last_update desc) r,
pa.company_id
from
postal_address pa
)
where company_id=c.company_id
AND r=1
) as Postcode
from device d,company c,
where d.company_id = c.company_id(+)
I have tried it with order the address withlast_update, but its getting me nothing back, where is my error? so i need the newest entry in the postal_address for my company_id.
Your row_number() analytic call is getting the row number across all companies, so you'll only get a match for the most-recently-changed company; no other company will get r = 1. You need to partition by the company ID:
row_number() over (partition by pa.company_id order by pa.last_update desc) r,
Or move the where company_id=c.company_id inside that nested subquery; but that doesn't work in some versions of Oracle (the c alias might not be visible).
I wouldn't use a subquery to get the column value within the select list at all here though; you could use the same row number check as an inline view and join to it:
select d.device, pa.postalcode_address
from device d
left join company c on c.company_id = d.company_id
left join (
select company_id, postalcode_address,
row_number() over (partition by company_id order by last_update desc) rn
from postal_address
) pa on pa.company_id = c.company_id and pa.rn = 1;
I have 3 tables: Master, Paper and iCodes. For a certain set of Master.Ref's, I need to find Max(Paper.Date), where the Paper.Code is also in the iCodes table (i.e., Paper.Code is a type of iCode). Master is joined to Paper by the File field.
EDIT:
I only need the Max(Paper.Date) its corresponding Code; I do not need all of the Codes.
I wrote the following but it is very slow. I have a few hundred ref #'s to look for. What is a better way to do this?
SELECT Master.Ref,
Paper.Code,
mp.MaxDate
FROM ( SELECT p.File ,
MAX(p.Date) AS MaxDate ,
FROM Paper AS p
LEFT JOIN Master AS m ON p.File = m.File
WHERE m.Ref IN ('ref1', 'ref2', 'ref3', 'ref4', 'ref5', 'ref6'... )
AND p.Code IN ( SELECT DISTINCT i.iCode
FROM iCodes AS i
)
GROUP BY p.File
) AS mp
LEFT JOIN Master ON mp.File = Master.File
LEFT JOIN Paper ON Master.File = Paper.File
AND mp.MaxDate = Paper.Date
WHERE Paper.Code IN ( SELECT DISTINCT iCodes.iCode
FROM iCodes
)
Does this do what you want?
SELECT m.Ref, p.Code, max(p.date)
FROM Master m LEFT JOIN
Paper
ON m.File = p.File
WHERE p.Code IN (SELECT DISTINCT iCodes.iCode FROM iCodes) and
m.Ref IN ('ref1','ref2','ref3','ref4','ref5','ref6'...)
GROUP BY m.Ref, p.Code;
EDIT:
To get the code on the max date, then use window functions:
select ref, code, date
from (SELECT m.Ref, p.Code, p.date
row_number() over (partition by m.Ref order by p.date desc) as seqnum
FROM Master m LEFT JOIN
Paper
ON m.File = p.File
WHERE p.Code IN (SELECT DISTINCT iCodes.iCode FROM iCodes) and
m.Ref IN ('ref1','ref2','ref3','ref4','ref5','ref6'...)
) mp
where seqnum = 1;
The function row_number() assigns a sequential number starting at 1 to a group of rows. The groups are defined by the partition by clause, so in this case everything with the same m.Ref value would be in a single group. Within the group, rows are assigned the number based on the order by clause. So, the one with the biggest date gets the value of 1. That is the row you want.
Like, there is top keyword in sql server 2005, how to select top 1 row in mysql if i have join on multiple table & want to retrieve extreme of each ID/column. Limit restricts the no. of row returns so it can't solve my problem.
SELECT v.*
FROM document d
OUTER APPLY
(
SELECT TOP 1 *
FROM version v
WHERE v.document = d.id
ORDER BY
v.revision DESC
) v
or
SELECT v.*
FROM document d
LEFT JOIN
(
SELECT *, ROW_NUMBER() OVER (PARTITION BY v.id ORDER BY revision DESC)
FROM version
) v
ON v.document = d.id
AND v.rn = 1
The latter is more efficient if your documents usually have few revisions and you need to select all or almost all documents; the former is more efficient if the documents have many revisions or you need to select just a small subset of documents.
Update:
Sorry, didn't notice the question is about MySQL.
In MySQL, you do it this way:
SELECT *
FROM document d
LEFT JOIN
version v
ON v.id =
(
SELECT id
FROM version vi
WHERE vi.document = d.document
ORDER BY
vi.document DESC, vi.revision DESC, vi.id DESC
LIMIT 1
)
Create a composite index on version (document, revision, id) for this to work fast.
If I understand you correctly, top doesn't solve your problem either. top is exactly equivalent to limit. What you are looking for is aggregate functions, like max() or min() if you want the extremes. for example:
select link_id, max(column_a), min(column_b) from table_a a, table_b b
where a.link_id = b.link_id group by link_id