Lets say we have a table Requests with structure:
user_id
product_id
count
With entries like:
1 1 5
1 2 6
1 1 3
2 1 7
2 1 3
2 2 5
I want to count how much of each product each user has.
And get output like this:
1 1 8
1 2 6
2 1 10
2 2 5
Use GROUP BY with the SUM aggregate function:
SELECT user_id, product_id, SUM(count) AS total
FROM Requests
GROUP BY user_id, product_id
Your query will look something like this:
SELECT user_id, product_id, SUM(`count`)
FROM Requests
GROUP BY user_id, product_id
I wouldn't name a field "count" if I had the choice, as it's a SQL function and could cause weird naming conflicts down the road.
You can find a tutorial on how to use GROUP BY here:
SQL GROUP BY statement
You can also find specific information on the syntax and use of GROUP BY in MySQL in the MySQL Manual:
MySQL SELECT Syntax
MySQL GROUP BY Functions And Modifiers
Related
Based on an example already given, I would like to ask my further question.
MySQL: Count occurrences of distinct values
example db
id name
----- ------
1 Mark
2 Mike
3 Paul
4 Mike
5 Mike
6 John
7 Mark
expected result
name count
----- -----
Mark 2
Mike 3
Paul 1
Mike 3
Mike 3
John 1
Mark 2
In my opinion 'GROUP BY' doesn't help.
Thank you very much.
Simplest approach would be using Count() as Window Function over a partition of name; but they are available only in MySQL 8.0.2 and onwards.
However, another approach is possible using a Derived Table. In a sub-select query (Derived Table), we will identify the counts for each unique name. Now, we simply need to join this to the main table, to show counts against each name (while not doing a grouping on them):
SELECT
t1.name,
dt.total_count
FROM your_table AS t1
JOIN
(
SELECT name,
COUNT(*) AS total_count
FROM your_table
GROUP BY name
) AS dt ON dt.name = t1.name
ORDER BY t1.id
If MySQL 8.0.2+ is available, the solution would be less verbose:
SELECT
name,
COUNT(*) OVER (PARTITION BY name) AS total_count
FROM your_table
I have 2 columns having users id participating in a transaction, source_id and destination_id. I'm building a function to sum all transactions grouped by any user participating on it, either as source or as destination.
The problem is, when I do:
select count (*) from transactions group by source_id, destination_id
it will first group by source, then by destination, I want to group them together. Is it possible using only SQL?
Sample Data
source_user_id destination_user_id
1 4
3 4
4 1
3 2
Desired result:
Id Count
4 - 3 (4 appears 3 times in any of the columns)
3 - 2 (3 appears 2 times in any of the columns)
1 - 2 (1 appear 2 times in any of the columns)
2 - 1 (1 appear 1 time in any of the columns)
As you can see on the example result, I want to know the number of times an id will appear in any of the 2 fields.
Use union all to get the id's into one column and get the counts.
select id,count(*)
from (select source_id as id from tbl
union all
select destination_id from tbl
) t
group by id
order by count(*) desc,id
edited to add: Thank you for clarifying your question. The following isn't what you need.
Sounds like you want to use the concatenate function.
https://dev.mysql.com/doc/refman/5.7/en/string-functions.html#function_concat
GROUP BY CONCAT(source_id,"_",destination_id)
The underscore is intended to distinguish "source_id=1, destination_id=11" from "source_id=11, destination_id=1". (We want them to be 1_11 and 11_1 respectively.) If you expect these IDs to contain underscores, you'd have to handle this differently, but I assume they're integers.
It may look like this.
Select id, count(total ) from
(select source_id as id, count (destination_user_id) as total from transactions group by source_id
union
select destination_user_id as id , count (source_id) as total from transactions group by destination_user_id ) q group by id
So I'm tasked with cleaning up a system that has generated redundant orders.
Data example of the problem
ORDER ID, SERIAL, ...
1 1
2 1
3 2
4 2
5 3
6 3
7 3
The above data shows that 2 orders were generated with serial 1, 2 orders with serial 2, and 3 orders with serial 3. This is not allowed, and there should be only one order per serial.
So I need a query that can identify the REDUNDANT orders ONLY. I'd like the query to exclude the original order.
So the output from the above data should be:
REDUNDANT ORDER IDS
2
4
6
7
I can easily identify which orders have duplicates using GROUP BY and HAVING COUNT(*) > 1 but the tricky part comes with removing the original.
Is it even possible?
Any help is greatly appreciated.
As posted in the comments, here's one way to achieve this:
SELECT T1.ORDER_ID as redundant
FROM thetable T1
LEFT JOIN
(
SELECT SERIAL, MIN(ORDER_ID) AS firstorder
FROM thetable
GROUP BY SERIAL
HAVING COUNT(*) > 1
) T2 ON T1.ORDER_ID=T2.firstorder
WHERE T2.firstorder IS NULL
SQL Fiddle
I have a database with one table as shown below. Here I'm trying to write a query to display the names of medication manufactured by the company that manufactures the most number of medications.
By looking at the table we could say the medication names which belongs to the company id 1 and 2 - because those company manufactures the most medication according to this table, but I'm not sure how to write a query for selecting the same i said before.
ID | COMPANY_ID | MEDICATION_NAME
1 1 ASPIRIN
2 1 GLUCERNA
3 2 SIBUTRAMINE
4 1 IBUPROFEN
5 2 VENOFER
6 2 AVONEN
7 4 ACETAMINOPHEN
8 3 ACETAMINO
9 3 GLIPIZIDE
Please share your suggestions. Thanks!
Several ways to do this. Here's one which first uses a subquery to get the maximum count, then another subquery to get the companies with that count, and finally the outer query to return the results:
select *
from yourtable
where companyid in (
select companyid
from yourtable
group by companyid
having count(1) = (
select count(1) cnt
from yourtable
group by companyid
order by 1 desc
limit 1
)
)
SQL Fiddle Demo
This Query might work. I have not tested but the logic is correct
SELECT MEDICATION_NAME
FROM TABLE where
COMPANY_ID=(SELECT
MAX(counted)
FROM ( SELECT COUNT(*) AS counted FROM TABLE ) AS counts);
I need to perform a query in MySQL that returns distinct values for product_id but also I need to select and return 'id' field which is in that particular table.
This query will return distinct product_id's without id:
SELECT DISTINCT product_id FROM orders_cart
This query will use distinct on both fields which and I want to use it on product_id and see the id
SELECT DISTINCT id, product_id FROM orders_cart
It would be quite easy to do on pgsql but I have no idea how to do this on mysql.
Your query is not well-defined: Consider this table
id product_id
1 1
2 2
3 1
4 2
What should your query result be? If you mean
id product_id
1 or 3 1
2 or 4 2
you are in the land of non-deterministic queries.
What you could do is
SELECT MIN(id), product_id FROM orders_cart GROUP BY product_id
which would deterministically produce
id product_id
1 1
2 2
Thats my final code:
The most important bits for this issue were line 1,2 and 4 :)
GROUP BY did the trick :)
SELECT orders_cart.id, product_id, order_id
FROM orders_cart
LEFT JOIN orders_order ON orders_cart.order_id=orders_order.id
WHERE orders_order.status='Wysłano'
GROUP BY orders_cart.product_id