Let's say i've got this database:
book
| idBook | name |
|--------|----------|
| 1 |Book#1 |
category
| idCateg| category |
|--------|----------|
| 1 |Adventures|
| 2 |Science F.|
book_categ
| id | idBook | idCateg | DATA |
|--------|--------|----------|--------|
| 1 | 1 | 1 | (null) |
| 2 | 1 | 2 | (null) |
I'm trying to select only the books which are in category 1 AND category 2
This is what I've got so far:
SELECT book.* FROM book,book_categ
WHERE book_categ.idCateg = 1 AND book_categ.idCateg = 2
Obviously, this giving 0 results becouse each row has only one idCateg it does work width OR but the results are not what I need. I've also tried to use a join, but I just can't get the results I expect.
Here it's the SQLFiddle of my current project, the data at the begining is just a sample.
SQLFiddle
Any help will be really appreciated.
You could double join with a constraint on the category id:
SELECT a.* FROM book AS a
INNER JOIN book_categ AS b ON a.idBook = b.idBook AND b.idCateg = 1
INNER JOIN book_categ AS c ON a.idBook = c.idBook AND c.idCateg = 2
You could use a subquery:
SELECT a.* FROM book AS a
WHERE
(SELECT COUNT(DISTINCT idCateg) FROM book_categ AS b
WHERE b.idBook = a.idBook AND b.idCateg IN (1,2)) = 2
If you are on MySQL as your fiddle implies, you should prefer the join variant, since most joins are much faster in MySQL than subqueries.
edit
This one should also work:
SELECT a.* FROM book a
INNER JOIN book_categ AS b ON a.idBook = b.idCateg
WHERE b.idCateg IN (5, 6)
GROUP BY idBook
HAVING COUNT(DISTINCT b.idCateg) = 2
and should be faster than the two above, although you have to change the last number according to the number of category ids you are requesting.
Related
I have this query in mySQL where I would like to sum the line product of each doctor but I dont know how to do it.
use avant_medical;
select
sales.doctor_id as DoctorID,
line_products.id as LineProductID,
line_products.name as LineProductName
from `doctors`
inner join `sales` on `doctors`.`id` = `sales`.`doctor_id`
inner join `inventories` on `sales`.`id` = `inventories`.`sale_id`
inner join `products` on `inventories`.`product_id` = `products`.`id`
inner join `line_products` on `products`.`lineProduct_id` = `line_products`.`id`
order by `doctors`.`id` asc;
lPID= lineProductID
|DrID|lPID |
| -- | ----|
| 1 | 7 |
| 1 | 6 |
| 1 | 6 |
| 1 | 7 |
| 1 | 7 |
| 1 | 7 |
| 1 | 6 |
This is how I want:
Doctor 1
lineID | quantity
7 | 4
6 | 3
I try this query only in mySQL
The keyword you are looking for is count, not sum. Summing would add up every lineProductID as if they where regular mathematical values, while counting will add up how many times a given lineProductID is found.
select
sales.doctor_id as DoctorID,
line_products.id as LineProductID,
line_products.name as LineProductName,
-- We count the number of occurrences of each line_product.id
COUNT(line_products.id) as LineProductQty
from `doctors`
inner join `sales` on `doctors`.`id` = `sales`.`doctor_id`
inner join `inventories` on `sales`.`id` = `inventories`.`sale_id`
inner join `products` on `inventories`.`product_id` = `products`.`id`
inner join `line_products` on `products`.`lineProduct_id` = `line_products`.`id`
-- Never forget to properly GROUP your aggregate functions, such as COUNT() or SUM()!
GROUP BY sales.doctor_id, line_products.id, line_products.name
order by `doctors`.`id` asc;
Since you didn't provided full schema to test this, I made a small, very artificial demo, but should be representative of how the query above works.
I've been trying for two days, without luck.
I have the following simplified tables in my database:
customers:
| id | name |
| 1 | andrea |
| 2 | marco |
| 3 | giovanni |
access:
| id | name_id | date |
| 1 | 1 | 5000 |
| 2 | 1 | 4000 |
| 3 | 2 | 1500 |
| 4 | 2 | 3000 |
| 5 | 2 | 1000 |
| 6 | 3 | 6000 |
| 7 | 3 | 2000 |
I want to return all the names with their last access date.
At first I tried simply with
SELECT * FROM customers LEFT JOIN access ON customers.id =
access.name_id
But I got 7 rows instead of 3 as expected. So I understood I need to use GROUP BY statemet as the following:
SELECT * FROM customers LEFT JOIN access ON customers.id =
access.name_id GROUP BY customers.id
As far I know, GROUP BY combines using a random row. In fact I got unordered access dates with several tests.
Instead I need to group every customer id with its corresponding latest access! How this can be done?
You have to get the latest date from the access table with a group by on the the name_id, then join this result with the customer table. Here is the query:
select c.id, c.name, a.last_access_date from customers c left join
(select id, name_id, max(access_date) last_access_date from access group by name_id) a
on c.id=a.name_id;
Here is a DEMO on sqlfiddle.
I think this is what you'd like to achieve:
SELECT c.id, c.name, max(a.date) last_access
FROM customers c
LEFT JOIN access a ON c.id = a.name_id
GROUP BY c.id, c.name
The LEFT join will return all entries in table customers regardless if the join criteria (c.id = a.name_id) is satisfied. This means that you might get some NULL entries.
Example:
Simply add a new row in the customers table (id: 4, name: manuela). The output will have 4 rows and the newest row will be (id: 4, last_access: null)
I would do this using a correlated subquery in the ON clause:
SELECT a.*, c.*
FROM customers c LEFT JOIN
access a
ON c.id = a.name_id AND
a.DATE = (SELECT MAX(a2.date) FROM access a2 WHERE a2.name_id = a.name_id);
If this statement is true:
I need to group every customer id with its corresponding latest access! How this can be done?
Then you can simply do:
select a.name_id, max(a2.date)
from access a
group by a.name_id;
You do not need the customers table because:
All customers are in access, so the left join is not necessary.
You need no columns from customers.
I have the following tables:
'blog_content'
'blog_media'
'blog_media_content'
| blog_id | media_id |
========================
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 3 | 4 |
I want to select all blog_media.uri's where blog_media.media_id equals blog_media_content.blog_id.
Please help me to achieve my aim.
An inner join between blog_media and blog_media_content tables would suffice.
SELECT
bm.uri
FROM blog_media bm
INNER JOIN blog_media_content bmc ON bm.media_id = bmc.media_id
WHERE bmc.blog_id =3;
Note:
If you need any additional information from blog table then you need an additional inner join like below:
...INNER JOIN blog_table b ON bmc.blog_id = b.blog_id...
EDIT:
In order to get records for all blog_ids :
SELECT
bm.uri
FROM blog_media bm
INNER JOIN blog_media_content bmc ON bm.media_id = bmc.media_id
ORDER BY bmc.blog_id;
I have the following (simplified) three tables:
user_reservations:
id | user_id |
1 | 3 |
1 | 3 |
user_kar:
id | user_id | szak_id |
1 | 3 | 1 |
2 | 3 | 2 |
szak:
id | name |
1 | A |
2 | B |
Now I would like to count the reservations of the user by the 'szak' name, but I want to have every user counted only for one szak. In this case, user_id has 2 'szak', and if I write a query something like:
SELECT sz.name, COUNT(*) FROM user_reservations r
LEFT JOIN user_kar k ON k.user_id = r.user_id
LEFT JOIN szak s ON r.szak_id = r.id
It will return two rows:
A | 2 |
B | 2 |
However I want to every reservation counted to only one szak (lets say the highest id only). I tried MAX(k.id) with HAVING, but seems uneffective.
I would like to know if there is a supported method for that in MySQL, or should I first pick all the user ID-s on the backend site first, check their maximum kar.user_id, and then count only with those, removing them from the id list, when the given szak is counted, and then build the data back together on the backend side?
Thanks for the help - I was googling around for like 2 hours, but so far, I found no solution, so maybe you could help me.
Something like this?
SELECT sz.name,
Count(*)
FROM (SELECT r.user_id,
Ifnull(Max(k.szak_id), -1) AS max_szak_id
FROM user_reservations r
LEFT OUTER JOIN user_kar k
ON k.user_id = r.user_id
GROUP BY r.user_id) t
LEFT OUTER JOIN szak sz
ON sz.id = t.max_szak_id
GROUP BY sz.name;
I'm trying to use the SUM function to count rows from 3 tables, which is however, not working effectively since when the total_files and total_notes are returned, they both are the same when there is at least one file and then total_files will take the same value as total_notes which I don't understand why it's doing that.
It should count the number of rows which is relevant to each record that will get return as a record list with a count of total files, total notes and total contacts assigned to the record per record row (the data of files, notes and contacts do not get displayed only counted).
My query is shown below:
SELECT rec.street_number,
rec.street_name,
rec.city,
rec.state,
rec.country,
rec.latitude,
rec.longitude,
LEFT(rec.description, 250) AS description,
usr.username,
usr.full_name,
ppl.person_id,
ppl.first_name,
ppl.last_name,
SUM(IF(rlk.record_id = rec.record_id, 1, 0)) AS total_contacts,
SUM(IF(files.record_id = rec.record_id, 1, 0)) AS total_files,
SUM(IF(notes.record_id = rec.record_id, 1, 0)) AS total_notes,
(
SELECT COUNT(DISTINCT rec.record_id)
FROM records rec
WHERE rec.marked_delete = 0 AND rec.is_archive = 0
) AS total_records
FROM
(
records rec
INNER JOIN members usr ON rec.user_id = usr.user_id
LEFT OUTER JOIN record_links rlk ON rec.record_id = rlk.record_id
LEFT OUTER JOIN people ppl ON ppl.person_id = rlk.person_id AND rlk.record_id = rec.record_id
LEFT OUTER JOIN files files ON files.record_id = rec.record_id
LEFT OUTER JOIN notes notes ON notes.record_id = rec.record_id
)
WHERE rec.marked_delete = 0 AND rec.is_archive = 0
GROUP BY rec.record_id
ORDER BY rec.submit_date DESC
LIMIT 0, 25
Basically as you can see there is three SUM which will count relevant rows that comes from those tables, but I seriously don't understand how total_files would be taking the same value as total_notes is there something wrong I'm doing here?
It's because rec is joined to both notes and files.
Suppose record 1 has 2 notes and 1 file, record 2 has two note and two files, and record 3 has a note but no files.
Then the table rec LEFT OUTER JOIN files ... LEFT OUTER JOIN notes will look like this:
+-----------+---------+---------+
| record_id | file_id | note_id |
+-----------+---------+---------+
| 1 | 1 | 1 |
| 1 | 2 | 1 |
| 2 | 3 | 2 |
| 2 | 3 | 3 |
| 2 | 4 | 2 |
| 2 | 4 | 3 |
| 3 | NULL | 4 |
+-----------+---------+---------+
Note how every file_id gets joined to every note_id (within the same record_id). Also, since you have SUM(IF(files.record_id = rec.record_id,1,0)) and the join condition is files.record_id = rec.record_id, you are actually counting COUNT(files)*COUNT(notes) per record_id.
I'd recommend you instead COUNT(DISTINCT files.id) and COUNT(DISTINCT records.id). The column in the COUNT would be your primary key on files/notes, not files.record_id:
SELECT rec.record_id,
COUNT(DISTINCT files.id) AS total_files,
COUNT(DISTINCT notes.id) AS total_notes
FROM rec
-- note: LEFT OUTER JOIN is the same as LEFT JOIN in MySQL
LEFT JOIN files ON files.record_id=rec.record_id
LEFT JOIN notes ON notes.record_id=rec.record_id
GROUP BY record_id
+-----------+-------------+-------------+
| record_id | total_files | total_notes |
+-----------+-------------+-------------+
| 1 | 2 | 1 |
| 2 | 2 | 2 |
| 3 | 0 | 1 |
+-----------+-------------+-------------+
Of course, adjust to your query as necessary (add in those extra columns/joins).