I have four tables and like to know how many locations and downloads a certain name has.
names and locations are connected via the names_locations table
Here are my tables:
Table "names"
ID | name
=========
1 | foo
2 | bar
3 | zoo
4 | luu
Table "locations"
ID | location
=============
1 | Hamburg
2 | New York
3 | Singapore
4 | Tokio
Table "names_locations"
ID | location_id | name_id
==========================
1 | 1 | 1
2 | 1 | 2
3 | 2 | 2
4 | 3 | 3
5 | 1 | 2
Table "downloads"
ID | name_id | timestamp
=========================
1 | 1 | 1394041682
2 | 4 | 1394041356
3 | 1 | 1394041573
4 | 3 | 1394041981
5 | 1 | 1394041683
Result should be:
ID | name | locations | downloads
=================================
1 | foo | 1 | 3
2 | bar | 3 | 0
3 | zoo | 1 | 1
4 | luu | 0 | 1
Here's my attempt (without the downloads column):
SELECT names.*,
Count(names_locations.location_id) AS location
FROM names
LEFT JOIN names_locations
ON names.ID = names_locations.name_id
GROUP BY names.ID
I think this would work.
SELECT n.id,
n.name,
COUNT(DISTINCT l.id) AS locations,
COUNT(DISTINCT d.id) AS downloads
FROM names n LEFT JOIN names_location nl
ON n.id = nl.name_id
LEFT JOIN downloads dl
ON n.id = dl.name_id
LEFT JOIN locations l
ON l.id = nl.location_id
GROUP BY n.id, n.name
All of those seem to work. here's another one.
SELECT
a.ID,
a.name,
COUNT(c.location) AS locations,
COUNT(d.timestamp) AS downloads
FROM names AS a
LEFT JOIN names_locations AS b on a.ID=b.name_id
LEFT JOIN locations AS c ON b.location_id=c.ID
LEFT JOIN downloads AS d ON a.ID=d.name_id
GROUP BY a.name
SELECT
t.id,t.n AS name,
count(location_id) AS locations,
t.downloads
FROM names_location
RIGHT JOIN
(SELECT
names.id AS id,
names.name AS n,
count(timestamp) AS downloads
FROM names
LEFT JOIN downloads ON names.id = downloads.name_id
GROUP BY id) AS t
ON t.id = names_location.name_id
GROUP BY t.id
Output:
+------+------+-----------+-----------+
| id | name | locations | downloads |
+------+------+-----------+-----------+
| 1 | foo | 1 | 3 |
| 2 | bar | 3 | 0 |
| 3 | zoo | 1 | 1 |
| 4 | luu | 0 | 1 |
+------+------+-----------+-----------+
4 rows in set (0.00 sec)
Related
I have a problem when I have to select everything from one table (persons) then count how many objects they own by counting their occurrences on other tables (pens, chairs, books)
The current data is as followed:
select * from persons;
+----+-------+
| id | name |
+----+-------+
| 1 | Alex |
| 2 | Brad |
| 3 | Cathy |
+----+-------+
select * from pens;
+----+-----------+
| id | person_id |
+----+-----------+
| 1 | 2 |
| 2 | 2 |
| 3 | 2 |
| 4 | 3 |
+----+-----------+
select * from chairs;
+----+-----------+
| id | person_id |
+----+-----------+
| 1 | 1 |
+----+-----------+
select * from books;
+----+-----------+
| id | person_id |
+----+-----------+
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
+----+-----------+
I want the result to be something like this
+----+-------+-----------------------+-------------------------+------------------------+
| id | name | count(pens.person_id) | count(chairs.person_id) | count(books.person_id) |
+----+-------+-----------------------+-------------------------+------------------------+
| 1 | Alex | 0 | 1 | 1 |
| 2 | Brad | 3 | 0 | 1 |
| 3 | Cathy | 1 | 0 | 1 |
+----+-------+-----------------------+-------------------------+------------------------+
I have tried using inner join and left outer join, but join gave me an empty set (since no person matches all of the objects) and left outer join gave me incorrect results:
> select persons.*, count(pens.person_id),count(chairs.person_id),count(books.person_id) from persons join pens on pens.person_id=persons.id join books on books.person_id=persons.id join chairs on chairs.person_id=persons.id group by persons.id;
Empty set (0.002 sec)
> select persons.*, count(pens.person_id),count(chairs.person_id),count(books.person_id) from persons left outer join pens on pens.person_id=persons.id left outer join books on books.person_id=persons.id left outer join chairs on chairs.person_id=persons.id group by persons.id;
# +----+-------+-----------------------+-------------------------+------------------------+
id | name | count(pens.person_id) | count(chairs.person_id) | count(books.person_id) |
# +----+-------+-----------------------+-------------------------+------------------------+
1 | Alex | 0 | 1 | 1 |
2 | Brad | 3 | 0 | 3 |
3 | Cathy | 1 | 0 | 1 |
# +----+-------+-----------------------+-------------------------+------------------------+
Any suggestions will be greatly appreciated, sorry if it's obvious, I'm fairly new at this.
Using a left join approach to subqueries on each table we can try:
SELECT
p.id,
p.name,
COALESCE(ps.cnt, 0) AS cnt_pens,
COALESCE(c.cnt, 0) AS cnt_chairs,
COALESCE(b.cnt, 0) AS cnt_books
FROM persons p
LEFT JOIN
(
SELECT person_id, COUNT(*) AS cnt
FROM pens
GROUP BY person_id
) ps
ON ps.person_id = p.id
LEFT JOIN
(
SELECT person_id, COUNT(*) AS cnt
FROM chairs
GROUP BY person_id
) c
ON c.person_id = p.id
LEFT JOIN
(
SELECT person_id, COUNT(*) AS cnt
FROM books
GROUP BY person_id
) b
ON b.person_id = p.id
ORDER BY
p.id;
I have 3 table inside my database, my first table is person table its store all person name, my second table is hobby table its store all hobby of all person,the third table is referensi table store all references person and hobby.
Tabel person : Tabel hobby : Tabel referensi :
----------------- ------------------ -------------------------------------
| id | name | | id | hobby | | id | ref_person | ref_hobby |
----------------- ------------------ -------------------------------------
| 1 | Rose | | 1 | Makan | | 1 | 1 | 1 |
| 2 | Lisa | | 2 | Renang | | 2 | 1 | 3 |
| 3 | Jisoo | | 3 | Nyanyi | | 3 | 1 | 4 |
| 4 | Jennie| | 4 | Youtube| | 4 | 3 | 5 |
----------------- | 5 | Masak | -------------------------------------
------------------
I want to count all hobby by that person
Example I want select Rose : Or I want select Jisoo :
--------------------------- ---------------------------
| id | hobby | count | | id | hobby | count |
--------------------------- ---------------------------
| 1 | Makan | 1 | | 1 | Makan | 0 |
| 2 | Renang | 0 | | 2 | Renang | 0 |
| 3 | Nyanyi | 1 | | 3 | Nyanyi | 0 |
| 4 | Youtube| 1 | | 4 | Youtube| 0 |
| 5 | Masak | 0 | | 5 | Masak | 1 |
--------------------------- ---------------------------
And so forth, how do I solve this problem?
This is my query that I write but doesn't seem to work, because only data with count greater than 0 is shown.
SELECT
hobby.id,
hobby.name,
count( referensi.id ) AS count
FROM
referensi
LEFT OUTER JOIN hobby ON hobby.id = referensi.ref_hobby
JOIN person ON referensi.ref_person = person.id
WHERE person.id = 1
GROUP BY
hobby.id
Thanks in advance.
To solve this you need to JOIN referensi to person, selecting only entries in referensi corresponding to the person of interest, and then RIGHT JOIN to hobby. If there is no matching entry, the output is 0, otherwise 1. For example, for person 1:
SELECT h.id,
h.hobby,
CASE WHEN r.id IS NULL THEN 0 ELSE 1 END AS count
FROM referensi r
JOIN person p ON p.id = r.ref_person AND p.id = 1
RIGHT JOIN hobby h ON h.id = r.ref_hobby
ORDER BY h.id
This can also be implemented with a correlated subquery:
SELECT h.id,
h.hobby,
EXISTS (SELECT * FROM referensi r WHERE r.ref_hobby = h.id AND r.ref_person = 1) AS count
FROM hobby h
If a person/hobby tuple can appear in the referensi table more than once, you do need to do a COUNT:
SELECT h.id,
h.hobby,
COUNT(r.id) AS count
FROM referensi r
JOIN person p ON p.id = r.ref_person AND p.id = 1
RIGHT JOIN hobby h ON h.id = r.ref_hobby
GROUP BY h.id
Output (for all three queries on your sample data):
id hobby count
1 Makan 1
2 Renang 0
3 Nyanyi 1
4 Youtube 1
5 Masak 0
Demo on SQLFiddle
You can try to use condition aggravate function with OUTER JOIN
setting condition in CASE WHEN
Query 1:
SELECT
hobby.id,
hobby.name,
COUNT(CASE WHEN person.id = 3 THEN 1 END) AS count
FROM
hobby
LEFT JOIN referensi ON hobby.id = referensi.ref_hobby
LEFT JOIN person ON referensi.ref_person = person.id
GROUP BY
hobby.id,
hobby.name
Results:
| id | name | count |
|----|---------|-------|
| 1 | Makan | 0 |
| 2 | Renang | 0 |
| 3 | Nyanyi | 0 |
| 4 | Youtube | 0 |
| 5 | Masak | 1 |
You want to start your joining from hobby table, and use LEFT JOINs to optionnaly bring up the matching records in other tables.
SELECT
h.id,
h.hobby,
count( p.id ) AS count
FROM
hobby h
LEFT JOIN referensi r ON h.id = r.ref_hobby
LEFT JOIN person p ON r.ref_person = p.id AND p.id = 1
WHERE p.name is NULL OR p.name = 'Rose'
GROUP BY h.id, h.hobby
It is also a good practice to use table aliases, I added them to your query.
Demo on DB Fiddle for user Rose :
| id | hobby | count |
| --- | ------- | ----- |
| 1 | Makan | 1 |
| 2 | Renang | 0 |
| 3 | Nyanyi | 1 |
| 4 | Youtube | 1 |
| 5 | Masak | 0 |
I have my 2 tables like this and I want to select course for categories table where id, i.e 1 , also with courses that has parent 1 as category.
I try something like:
SELECT id,category,( (SELECT id FROM courses WHERE id = 1 OR parent = 1) AS selection) FROM courses
WHERE category IN selection;
But is not a right syntax, and also I would say I miss puttting into string comma separated to do something like that.
table categories
+----+--------+------+
| id | parent | path |
+----+--------+------+
| 1 | 0 | /1 |
| 2 | 1 | /1/2 |
+----+--------+------+
table courses
+----+----------+-----------+
| id | category | shortname |
+----+----------+-----------+
| 1 | 0 | MB2.9.8 |
| 2 | 2 | 1 c |
| 3 | 2 | 2 c |
| 4 | 1 | c 3 |
+----+----------+-----------+
Which means I would have this when I just send category id = 1 , because categories.parent on id "2" has "1" as parent too so selection of courses for 1 and 2 categories
+----+----------+-----------+
| id | category | shortname |
+----+----------+-----------+
| 2 | 2 | 1 c |
| 3 | 2 | 2 c |
| 4 | 1 | c 3 |
+----+----------+-----------+
You need a join
select CO.*
from Courses CO
inner join Categories CA
on CA.Category = CO.Id
or CA.Category = CO.Parent
where CA.ID = 1
or CA.Parent = 1
or an EXISTS:
select CO.*
from Courses CO
where exists (
select Id
from Category CA
where (CA.Parent = CO.Category
or CA.Id = CO.Category)
and (CA.ID = 1
or CA.Parent = 1)
)
This must be quite easy, but I cannot find a good solution myself.
I have two tables:
file
+----+--------+
| id | system |
+----+--------+
| 1 | AA |
| 2 | AA |
| 3 | BB |
| 4 | AA |
+----+--------+
feature
+----+---------+------+
| id | file_id | name |
+----+---------+------+
| 1 | 1 | A |
| 1 | 2 | A |
| 1 | 2 | B |
| 1 | 3 | B |
| 1 | 3 | C |
| 1 | 4 | A |
| 1 | 4 | B |
| 1 | 4 | C |
+----+---------+------+
and I want to count how many times a feature was added to files with a specific system. For that, I have the following query:
SELECT f.name, COUNT(*) AS nr
FROM dossier d
JOIN feature f
ON f.file_id = d.id
WHERE d.system = 'AA'
AND d.id NOT IN (3157,3168,3192)
GROUP BY f.name
which gives the desired output:
+------+----+
| name | nr |
+------+----+
| A | 3 |
| B | 2 |
| C | 1 |
+------+----+
Now I also want to know the total amount of files with the same specific system. A simple separate query would be:
SELECT COUNT(*) FROM file WHERE system = 'AA' AND id NOT IN (3157,3168,3192)
I've added the extra AND id NOT IN (which is irrelevant for this example) just to show that the actual query is much more complex. If I use a separate query to get the total I would have to duplicate that complexity, so I want to avoid that by returning the total from the same query.
So how can I count the number of files in the first query?
Desired output:
+------+----+-------+
| name | nr | total |
+------+----+-------+
| A | 3 | 3 |
| B | 2 | 3 |
| C | 1 | 3 |
+------+----+-------+
Here is one way using Sub-query
SELECT f.NAME,
Count(*) AS nr,
(SELECT Count(*)
FROM FILE
WHERE system = 'AA'
AND id NOT IN ( 3157, 3168, 3192 )) as Total
FROM dossier d
JOIN feature f
ON f.file_id = d.id
WHERE d.system = 'AA'
AND d.id NOT IN ( 3157, 3168, 3192 )
GROUP BY f.NAME
Or Use CROSS JOIN
SELECT *
FROM (SELECT f.NAME,
Count(*) AS nr,
FROM dossier d
JOIN feature f
ON f.file_id = d.id
WHERE d.system = 'AA'
AND d.id NOT IN ( 3157, 3168, 3192 )
GROUP BY f.NAME) A
CROSS JOIN (SELECT Count(*) AS Total
FROM FILE
WHERE system = 'AA'
AND id NOT IN ( 3157, 3168, 3192 )) B
I have two table and like to know how many downloads a certain name has. Here are my tables
Table "names"
ID | name
==========
1 | foo
2 | bar
3 | zoo
4 | luu
Table "downloads"
ID | name_id | timestamp
=========================
1 | 1 | 1394041682
2 | 4 | 1394041356
3 | 1 | 1394041573
4 | 3 | 1394041981
5 | 1 | 1394041683
Result should be:
ID | name | downloads
=====================
1 | foo | 3
2 | bar | 0
3 | zoo | 1
4 | luu | 1
This should be pretty easy...
It is pretty easy.
Just JOIN tables and COUNT rows. Don't forget to GROUP BY, and COUNT(timestamp) so you could get zero if there isn't any
SELECT n.ID,
n.name,
COUNT(timestamp) as downloads
FROM names n
LEFT JOIN downloads d
ON d.name_id = n.id
GROUP BY n.ID,
n.name
ORDER BY n.ID;
SQL Fiddle