I want to show all the photos that have the specific tag, but it only duplicates the photos. If I choose another tag, it doesn't show duplicated photos.
For the tag "Natur" it should only be 2 photos and for the tag "Berg" it should only be 1 photo.
SQL
SELECT *
FROM photos AS p
JOIN tags_photos AS tp
JOIN tags_names AS tn
ON tp.id_tag = tn.id
WHERE tn.data_name_seo = :name_seo
ORDER BY p.datetime_taken DESC
Database: tags_photos
id
id_photo
id_tag
Database: tags_name
id
data_name
data_name_seo
Database: photos
id
data_file_name
datetime_taken
Have I missed something or what's the problem?
You are missing join conditions for the first two tables. This is probably the cause of your problem:
SELECT *
FROM photos AS p JOIN
tags_photos AS tp
ON tp.id_photo = p.id JOIN
tags_names AS tn
ON tp.id_tag = tn.id
WHERE tn.data_name_seo = :name_seo
ORDER BY p.datetime_taken DESC
In most databases, the missing on clause would generate an error. In MySQL, the JOIN is treated as a CROSS JOIN, which likely would result in duplicates.
Related
i have following sql in java project:
select distinct * from drivers inner join licenses on drivers.user_id=licenses.issuer_id
inner join users on drivers.user_id=users.id
where (licenses.state='ISSUED' or drivers.status='WAITING')
and users.is_deleted=false
And result i database looks like this:
And i would like to get only one result instead of two duplicated results.
How can i do that?
Solution 1 - That's Because one of data has duplicate value write distinct keyword with only column you want like this
Select distinct id, distinct creation_date, distinct modification_date from
YourTable
Solution 2 - apply distinct only on ID and once you get id you can get all data using in query
select * from yourtable where id in (select distinct id from drivers inner join
licenses
on drivers.user_id=licenses.issuer_id
inner join users on drivers.user_id=users.id
where (licenses.state='ISSUED' or drivers.status='WAITING')
and users.is_deleted=false )
Enum fields name on select, using COALESCE for fields which value is null.
usually you dont query distinct with * (all columns), because it means if one column has the same value but the rest isn't, it will be treated as a different rows. so you have to distinct only the column you want to, then get the data
I suspect that you want left joins like this:
select *
from users u left join
drivers d
on d.user_id = u.id and d.status = 'WAITING' left join
licenses l
on d.user_id = l.issuer_id and l.state = 'ISSUED'
where u.is_deleted = false and
(d.user_id is not null or l.issuer_id is not null);
I am trying to get related products but the issue which I'm facing is that there is product photos table which has one-to-many relationship with products table, so when I get products by matching category Id it also returns multiple product photos with that product which i do not want. I want only one product photo from product photos table of specific product. Is there any way to use distinct in joins or any other way? what I have done so far....
SELECT [Product].[ID],
,[Thumbnail]
,[ProductName]
,[Model]
,[SKU]
,[Price]
,[IsExclusive]
,[DiscountPercentage]
,[DiscountFixed]
,[NetPrice]
,[Url]
FROM [dbo].[Product]
INNER JOIN [ProductPhotos] ON [ProductPhotos].[ProductID]=[Product].[ID]
INNER JOIN [ProductCategories] ON [ProductCategories].[ProductID]=
[Product].[ID]
WHERE [ProductCategories].[CategoryID]=4
And the result I am getting is...
Product Photos table has
Is there any way to use distinct or group by on product Id column in product photos table to return only one row from photos table.
Instead of using inner join, use cross apply:
SELECT . . .
FROM dbo.Product p CROSS APPLY
(SELECT TOP (1) pp.*
FROM ProductPhotos pp
WHERE pp.ProductID = p.id
ORDER BY NEW_ID()
) pp INNER JOIN
ProductCategories pc
ON pc.ProductID = p.id
WHERE pc.CategoryID = 4;
Notes:
The ORDER BY NEWID() chooses a random photo. You can order by specific columns to get the earliest, latest, biggest, or whatever.
Note that I added table aliases. These make the query easier to write and to read.
You should qualify all column names in your query, so it is clear which tables they come from.
I removed the superfluous square braces. They just make the query harder to write and to read.
You can use ROW_NUMBER() to return one row for ProductID, like this:
JOIN (SELECT *,
ROW_NUMBER() OVER (PARTITION BY ProductID ORDER BY PhotoID) rn
FROM [ProductPhotos]) [ProductPhotos]
ON [ProductPhotos].[ProductID]=[Product].[ID] AND [ProductPhotos].rn = 1
Instead of this:
JOIN [ProductPhotos] ON [ProductPhotos].[ProductID]=[Product].[ID]
you can use sub query in join with distinct instead of joining table directly.
you can create alias and use that column as distinct in select statement, but it will create performance issues when having loads of data inside.
if you have 3 different photos for same product Id (like 2). you can use sub-query with top 1 order by PK desc to get latest picture.
I want to be able to use unnest() function in PostgreSQL in a complicated SQL query that has many JOINs. Here's the example query:
SELECT 9 as keyword_id, COUNT(DISTINCT mentions.id) as total, tags.parent_id as tag_id
FROM mentions
INNER JOIN taggings ON taggings.mention_id = mentions.id
INNER JOIN tags ON tags.id = taggings.tag_id
WHERE mentions.taglist && ARRAY[9] AND mentions.search_id = 3
GROUP BY tags.parent_id
I want to eliminate the taggings table here, because my mentions table has an integer array field named taglist that consists of all linked tag ids of mentions.
I tried following:
SELECT 9 as keyword_id, COUNT(DISTINCT mentions.id) as total, tags.parent_id as tag_id
FROM mentions
INNER JOIN tags ON tags.id IN (SELECT unnest(taglist))
WHERE mentions.taglist && ARRAY[9] AND mentions.search_id = 3
GROUP BY tags.parent_id
This works but brings different results than the first query.
So what I want to do is to use the result of the SELECT unnest(taglist) in a JOIN query to compensate for the taggings table.
How can I do that?
UPDATE: taglist is the same set as the respective list of tag ids of mention.
Technically, your query might work like this (not entirely sure about the objective of this query):
SELECT 9 AS keyword_id, count(DISTINCT m.id) AS total, t.parent_id AS tag_id
FROM (
SELECT unnest(m.taglist) AS tag_id
FROM mentions m
WHERE m.search_id = 3
AND 9 = ANY (m.taglist)
) m
JOIN tags t USING (tag_id) -- assumes tag.tag_id!
GROUP BY t.parent_id;
However, it seems to me you are going in the wrong direction here. Normally one would remove the redundant array taglist and keep the normalized database schema. Then your original query should serve well, only shortened the syntax with aliases:
SELECT 9 AS keyword_id, count(DISTINCT m.id) AS total, t.parent_id AS tag_id
FROM mentions m
JOIN taggings mt ON mt.mention_id = m.id
JOIN tags t ON t.id = mt.tag_id
WHERE 9 = ANY (m.taglist)
AND m.search_id = 3
GROUP BY t.parent_id;
Unravel the mystery
<rant>
The root cause for your "different results" is the unfortunate naming convention that some intellectually challenged ORMs impose on people.
I am speaking of id as column name. Never use this anti-pattern in a database with more than one table. Right, that means basically any database. As soon as you join a bunch of tables (that's what you do in a database) you end up with a bunch of columns named id. Utterly pointless.
The ID column of a table named tag should be tag_id (unless there is another descriptive name). Never id.
</rant>
Your query inadvertently counts tags instead of mentions:
SELECT 25 AS keyword_id, count(m.id) AS total, t.parent_id AS tag_id
FROM (
SELECT unnest(m.taglist) AS id
FROM mentions m
WHERE m.search_id = 4
AND 25 = ANY (m.taglist)
) m
JOIN tags t USING (id)
GROUP BY t.parent_id;
It should work this way:
SELECT 25 AS keyword_id, count(DISTINCT m.id) AS total, t.parent_id
FROM (
SELECT m.id, unnest(m.taglist) AS tag_id
FROM mentions m
WHERE m.search_id = 4
AND 25 = ANY (m.taglist)
) m
JOIN tags t ON t.id = m.tag_id
GROUP BY t.parent_id;
I also added back the DISTINCT to your count() that got lost along the way in your query.
Something like this should work:
...
tags t INNER JOIN
(SELECT UNNEST(taglist) as idd) a ON t.id = a.idd
...
I'm building a system in which there are the following tables:
Song
Broadcast
Station
Follow
User
A user follows stations, which have songs on them through broadcasts.
I'm building a "feed" of songs for a user based on the stations they follow.
Here's the query:
SELECT DISTINCT ON ("broadcasts"."created_at", "songs"."id") songs.*
FROM "songs"
INNER JOIN "broadcasts" ON "songs"."shared_id" = "broadcasts"."song_id"
INNER JOIN "stations" ON "broadcasts"."station_id" = "stations"."id"
INNER JOIN "follows" ON "stations"."id" = "follows"."station_id"
WHERE "follows"."user_id" = 2
ORDER BY broadcasts.created_at desc
LIMIT 18
Note: shared_id is the same as id.
As you can see I'm getting duplicate results, which I don't want. I found out from a previous question that this was due to selecting distinct on broadcasts.created_at.
My question is: How do I modify this query so it will return only unique songs based on their id but still order by broadcasts.created_at?
Try this solution:
SELECT a.maxcreated, b.*
FROM
(
SELECT bb.song_id, MAX(bb.created_at) AS maxcreated
FROM follows aa
INNER JOIN broadcasts bb ON aa.station_id = bb.station_id
WHERE aa.user_id = 2
GROUP BY bb.song_id
) a
INNER JOIN songs b ON a.song_id = b.id
ORDER BY a.maxcreated DESC
LIMIT 18
The FROM subselect retrieves distinct song_ids that are broadcasted by all stations the user follows; it also gets the latest broadcast date associated with each song. We have to encase this in a subquery because we have to GROUP BY on the columns we're selecting from, and we only want the unique song_id and the maxdate regardless of the station.
We then join that result in the outer query to the songs table to get the song information associated with each unique song_id
You can use Common Table Expressions (CTE) if you want a cleaner query (nested queries make things harder to read)
I would look like this:
WITH a as (
SELECT bb.song_id, MAX(bb.created_at) AS maxcreated
FROM follows aa
INNER JOIN broadcasts bb ON aa.station_id = bb.station_id
INNER JOIN songs cc ON bb.song_id = cc.shared_id
WHERE aa.user_id = 2
GROUP BY bb.song_id
)
SELECT
a.maxcreated,
b.*
FROM a INNER JOIN
songs b ON a.song_id = b.id
ORDER BY
a.maxcreated DESC
LIMIT 18
Using a CTE offers the advantages of improved readability and ease in maintenance of complex queries. The query can be divided into separate, simple, logical building blocks. These simple blocks can then be used to build more complex, interim CTEs until the final result set is generated.
Try by adding GROUP BY Songs.id
I had a very similar query I was doing between listens, tracks and albums and it took me a long while to figure it out (hours).
If you use a GROUP_BY songs.id, you can get it to work by ordering by MAX(broadcasts.created_at) DESC.
Here's what the full SQL looks like:
SELECT songs.* FROM "songs"
INNER JOIN "broadcasts" ON "songs"."shared_id" = "broadcasts"."song_id"
INNER JOIN "stations" ON "broadcasts"."station_id" = "stations"."id"
INNER JOIN "follows" ON "stations"."id" = "follows"."station_id"
WHERE "follows"."user_id" = 2
GROUP BY songs.id
ORDER BY MAX(broadcasts.created_at) desc
LIMIT 18;
I'm learning advanced SQL queries little by little and I'm fairly stumped with a problem:
I have three tables: news, author, and images. Each field in the news table (newsID) is a news story, which then has an associated author in the author table (authorID) and can have any number of images associated in the images table. Each image has and associated (newsID). So each story has one author but can have several images.
I want to make a list of all news stories and use just one of the images as a thumbnail image. The problem is that any sql query I try to list the news items with gives me results equal to the number of images in the images table rather than the number of news items.
I don't know where to go from here. Any help would be greatly appreciated.
If the 3 tables in question are [news], [author] and [image] with appropriate columns, then
Derived Table approach
you can have a derived image table to get one image per news and then join it with the news and author table as shown.
This has been written and tested in SQL Server.
SELECT
N.[newsStoryTitle]
,A.authorName
,I.imageData1
FROM [news] N
LEFT OUTER JOIN author A ON A.newsID = N.newsID
LEFT OUTER JOIN
(
SELECT newsID, MAX(imageData) AS imageData1 FROM [image]
GROUP BY newsID
) AS I ON I.newsID = N.newsID
ORDER BY N.newsID
You could replace the LEFT OUTER JOINs with INNER JOINs if you do not need news without any images.
Correlated Subquery approach (as suggested by Marcelo Cantos)
If the imageData is stored as a text or image, then the MAX in the derived table wouldn't work. In that case, you can use a correlated subquery like this:
SELECT N.newsStoryTitle ,
A.authorName ,
I.imageData
FROM dbo.news N
INNER JOIN dbo.author A ON N.newsID = A.newsID
INNER JOIN dbo.image I ON N.newsID = I.newsID
WHERE imageID = ( SELECT MAX(imageID)
FROM dbo.image
WHERE newsID = N.newsID
)
ORDER BY n.newsID
One option is to add the following predicate:
FROM news JOIN images ...
...
WHERE imageID = (SELECT MAX(imageID)
FROM image
WHERE newsID = news.newsID)
Note that this excludes news items without an image. If you don't want this, you'll need a left join on images and an additional condition on the WHERE:
FROM news LEFT JOIN images ...
...
WHERE imageID IS NULL
OR imageID = (SELECT MAX(imageID)
FROM image
WHERE newsID = news.newsID)
You can to modify the order by on the subselect to get the 1 image per news row you are looking for...
select
....
from news n
left outer join images i on i.imageID = (
select top 1 i2.imageID
from images i2
where i2.newsID = n.newsID
order by --??
)
If you have 3 table in mysql and you want to join it together. for example I have 3 table
1 student
2 subject
3 score
now want to join student with subject and score. so we you this syntax :
select * from student inner join subject inner join score;