Ok, I have three tables, Colors,People,Likes
Colors contains ids and names colors, People contains ids and names of people, Likes contains color_id and people_id to describe which people like which colors.
Now, given a list of colors, how can I select every person (if any) who likes every color in the list?
select p.id, p.name
from people p
join likes l on l.people_id = p.id
join colors c on l.color_id = c.id
where c.name in ('blue','green','red')
group by p.id, p.name
having count(distinct c.name) = 3
You can GROUP BY the person joined on the Likes, and retrieve those tuples HAVING a COUNT(*) equal to the number of rows in the Color list. This way you
only need to join two tables
don't need to explicitly name the colors.
SELECT People.id, COUNT(*) AS ColorsLiked
FROM People JOIN Likes ON (People.id = Likes.people_id)
GROUP BY People.id
HAVING ColorsLiked = (SELECT COUNT(*) FROM Colors);
SELECT * FROM People p
INNER JOIN Likes l ON l.people_id = p.people_id
INNER JOIN Colors c ON l.color_id = c.color_id
WHERE c.name IN ('List of colors')
Related
I have two tables: users and courses. Inside users table i have filed course where i have course id. Inside courses table i have just ID and NAME.
I need to get popular course. I do request:
SELECT u.course, COUNT(*) as freq FROM users u INNER JOIN courses c ON u.course = c.id GROUP BY u.course
As a result: id => freq. But i need to replace ID to NAME of course. How?
Thanks.
You don't say what database you use, but I would assume you can use CTEs since most modern databases do. Your query can be written as:
with x as (
select course, count(*) as freq from users group by course
),
y as (
select max(freq) as max_freq from x
)
select c.name, x.freq
from x
join y on x.freq = y.max_freq
join courses c on c.id = x.course
This query has the [desirable?] side effect that it shows more than one course, if there are more than one tied in first place.
Add c.name to both the SELECT clause and the GROUP BY clause.
SELECT u.course, c.name, COUNT(*) as freq
FROM users u
INNER JOIN courses c
ON u.course = c.id
GROUP BY u.course, c.name;
Demo: https://dbfiddle.uk/?rdbms=mariadb_10.3&fiddle=02a41e0f1e6407e516e91c49b4bdc1d2
SELECT u.course, COUNT(*) as freq, c.name FROM users u INNER JOIN courses c ON u.course = c.id GROUP BY u.course
If your DBMS supports row_number this will be suitable:
select t.id, c.name, t.cnt
from course c
join (
select c.id, count(1) cnt, ROW_NUMBER() over(order by count(1) desc) rn
from users u
join course c on c.id = u.course
group by id
)t on t.id = c.id and t.rn = 1
Please i have four tables joined together using the LEFT JOIN, the images table is linked to the items table by img_item, thus each item can have more images. i want to fetch only the first image of every item. How do i go achieve this.
SELECT * FROM items
LEFT JOIN category ON items.item_cat = category.cat_id
LEFT JOIN users ON users.user_id=items.item_user
LEFT JOIN institutions ON institutions.inst_id=users.user_inst
LEFT JOIN images ON images.img_item = items.item_id
ORDER BY item_id DESC
In MySQL, you can enumerate the results using variables, and then choose the first. Another alternative is to identify which one you want, and choose that one. The following chooses the image with the largest id:
SELECT *
FROM items LEFT JOIN
category
ON items.item_cat = category.cat_id LEFT JOIN
users
ON users.user_id=items.item_user LEFT JOIN
institutions
ON institutions.inst_id = users.user_inst LEFT JOIN
images
ON images.img_item = items.item_id AND
images.img_id = (SELECT MAX(i2.img_id)
FROM images i2
WHERE i2.img_item = images.img_item
);
ORDER BY item_id DESC
I have a MYSQL query who have to list all post i want it to post. But it dont do it. It shows posts when i have more then one post in the table "meaOrder" with the same "ordCode". But when i have only on post in meaOrder, i don't show it. What can i do?
SELECT koden, wish, rnamn, bild, pris, cname, onsktext
FROM (
SELECT m.wishText as onsktext, m.meaOID as midn, m.ordcode as koden, w.wish as wish, r.meaName as rnamn, r.meaImg as bild,
r.meaPrice as pris, k.catName as cname from cats k, meals r, wishes w,
meaOrder m
join orders c on c.ordNR=4401
WHERE c.ordStatus=1 AND m.ordNR=c.ordNR AND m.meaID=r.meaID AND m.wishesID=w.id
AND r.catID=k.catID
) T
GROUP BY koden, rnamn, bild, pris, cname
ORDER BY midn DESC
TABLE orders
http://grab.by/m74E
TABLE meaOrder http://grab.by/m74Q
Try replacing the JOIN with RIGHT JOIN in this case. The difference is explained at JOIN Syntax page in MySQL docs . In short - JOIN returns row only if there are corresponding rows in both joined tables (inner join). LEFT JOIN / RIGHT JOIN return all rows from one of the tables and corresponding row if it exists from the other table (those are outer joins)
Do you need a subselect?
This seems to cover it:-
SELECT m.ordcode AS koden, w.wish AS wish, r.meaName AS rnamn, r.meaImg AS bild, r.meaPrice AS pris, k.catName AS cname, m.wishText AS onsktext
FROM cats k
INNER JOIN meals r ON r.catID = k.catID
INNER JOIN meaOrder m ON m.meaID = r.meaID
INNER JOIN wishes w ON m.wishesID = w.id
INNER JOIN orders c ON m.ordNR = c.ordNR
WHERE c.ordStatus = 1
AND c.ordNR = 4401
GROUP BY m.ordcode, r.meaName, r.meaImg, r.meaPrice, k.catName
ORDER BY midn DESC
I'm really sorry for the first post as i didn't explain everything.
Basically i have 3 tables, One for posts, One for Categories, & Another to link categories with posts.
I want in a single MySQL query to select posts that are under a specific category.
posts(id,title,body)
---------------------
125,Some title,Blah blah
categories(id,name)
---------------------
1,politic
2,entertainment
linker(categoryid,postid)
---------------------
2,125
I want in single query to fetch posts in the entertainment category by example, what to do?
Thanks
select
p.*
from
posts p
inner join linker l on l.postid = p.id
inner join categories c on c.categoryid = l.categoryid
where
c.name = 'entertainment'
The following SQL statement should provide you with a basis for what you are trying to do.
select p.*
from posts p
inner join linker l
on l.postid = p.id
inner join categories c
on l.categoryid = c.id
where c.name = 'entertainment'
If a post belongs to 2 categories, you can still use pinkfloydx33's query with DISTINCT in the select statement:
select
DISTINCT p.*
from
posts p
inner join linker l on l.postid = p.id
inner join categories c on c.categoryid = l.categoryid
where
c.name = 'entertainment'
The result set will show only one record.
It's the same exact thing, you just have to join 3 tables intead of 2 :
SELECT P.id post_id,
P.title,
P.body,
C.id category_id,
C.name
FROM posts P
INNER JOIN linker L
ON P.id = L.postid
INNER JOIN categories C
ON L.categoryid = C.id
WHERE C.name = 'Category'
Don't be afraid to do your own tests. If you understand how to join two tables, you should understand how to join three, four and more.
If you are specifying only one category in the WHERE clause, then the result will be a single row for each post ID.
Either way you can use DISTINCT or GROUP BY when the result could be more than one row per ID, but in that case i prefer the second one (GROUP BY).
I have a table containing persons information (one row per person) and another table containing persons photos filenames (many rows per person). I want to select a group of persons (based on another table) but only one photo per person.
My old SQL was like this:
SELECT persons.personID, persons.name, persons.photo_filename, movie_cast.role
FROM persons, movie_cast
WHERE persons.personID = movie_cast.personID
AND movie_cast.imdbID = ?
ORDER BY movie_cast.castORDER
LIMIT 9';
But here, the 'persons' table contains also a 'photo_filename' column. In my new database design, this column is in another table. So if I try to get the photo_filename from the new table I get all the photos available for each person, but I need to get only one.
How to do it?
In the first example I have assumed there is always a photo, and am just grabbing the highest sorted photo filename alphabetically as a means to get a consistent photo for each user each time you run the query.
SELECT p.personID, p.name, ph.photo_filename, mc.role
FROM persons p
INNER JOIN movie_cast mc ON p.personID = mc.personID
INNER JOIN (
select personID, max(photo_filename) as MaxPhotoName
from photos
group by personID
) phm on p.personID = phm.personID
INNER JOIN photos ph on phm.personID = ph.personID
and phm.MaxPhotoName = ph.photo_filename
WHERE mc.imdbID = ?
ORDER BY mc.cast
LIMIT 9
If there is a photo_date column and you want to use the newest photo you can do it like this:
SELECT p.personID, p.name, ph.photo_filename, mc.role
FROM persons p
INNER JOIN movie_cast mc ON p.personID = mc.personID
INNER JOIN (
select personID, max(photo_date) as MaxPhotoDate
from photos
group by personID
) phm on p.personID = phm.personID
INNER JOIN photos ph on phm.personID = ph.personID
and phm.MaxPhotoDate = ph.photo_date
WHERE mc.imdbID = ?
ORDER BY mc.cast
LIMIT 9
If there is not always a photo, you can use a LEFT OUTER JOIN so that you will still get all your records back:
SELECT p.personID, p.name, ph.photo_filename, mc.role
FROM persons p
INNER JOIN movie_cast mc ON p.personID = mc.personID
LEFT OUTER JOIN (
select personID, max(photo_date) as MaxPhotoDate
from photos
group by personID
) phm on p.personID = phm.personID
LEFT OUTER JOIN photos ph on phm.personID = ph.personID
and phm.MaxPhotoDate = ph.photo_date
WHERE mc.imdbID = ?
ORDER BY mc.cast
LIMIT 9