I need some help with counting both unique and duplicate values in MySQL. I want to know how many records there are total, and also how many is there two times and three times and so on...
Do I need to use UNION or something? I think SUM would be the best solution for me because of I might use some joins with this in future.
Sample data:
| custId | name |
|--------|--------|
| 1001 | Alex |
| 1001 | Alex |
| 1002 | Daniel |
| 1003 | Mark |
| 1002 | Daniel |
Sample results:
| total | twoTimes | threeTimes |
|-------|----------|------------|
| 3 | 2 | 0 |
Thanks in advance.
Just a basic group by should do it
SELECT YourValue, Count(YourValue)
FROM YourTable
GROUP BY YourValue
If you want only a category, like unique values ADD
HAVING Count(YourValue) = 1
Here is my approach:
http://sqlfiddle.com/#!9/9411dc/3
SELECT c.cnt AS `times`, COUNT(c.name) cnt
FROM (SELECT name, COUNT(custId) cnt
FROM cust
GROUP BY name) c
GROUP BY c.cnt;
that is not exactly what you did ask (you asked for pivot table which is very difficult to realize). So if you want to make it pivot you can read here: MySQL pivot table
And if you are sure that you have very small max of duplicate count your pivot query could be:
http://sqlfiddle.com/#!9/9411dc/5
SELECT
SUM(IF(c.cnt=1,1,0)) AS `Unique`,
SUM(IF(c.cnt=2,1,0)) AS `Two times`,
SUM(IF(c.cnt=3,1,0)) AS `Three times`,
SUM(IF(c.cnt=4,1,0)) AS `Four times`
FROM (SELECT name, COUNT(custId) cnt
FROM cust
GROUP BY name) c
Related
I'm very average with MySQL, but usually I can write all the needed queries after reading documentation and searching for examples. Now, I'm in the situation where I spent 3 days re-searching and re-writing queries, but I can't get it to work the exact way I need. Here's the deal:
1st table (mpt_companies) contains companies:
| company_id | company_title |
------------------------------
| 1 | Company A |
| 2 | Company B |
2nd table (mpt_payment_methods) contains payment methods:
| payment_method_id | payment_method_title |
--------------------------------------------
| 1 | Cash |
| 2 | PayPal |
| 3 | Wire |
3rd table (mpt_payments) contains payments for each company:
| payment_id | company_id | payment_method_id | payment_amount |
----------------------------------------------------------------
| 1 | 1 | 1 | 10.00 |
| 2 | 2 | 3 | 15.00 |
| 3 | 1 | 1 | 20.00 |
| 4 | 1 | 2 | 10.00 |
I need to list each company along with many stats. One of stats is the sum of payments in each payment method. In other words, the result should be:
| company_id | company_title | payment_data |
--------------------------------------------------------
| 1 | Company A | Cash:30.00,PayPal:10.00 |
| 2 | Company B | Wire:15.00 |
Obviously, I need to:
Select all the companies;
Join payments for each company;
Join payment methods for each payment;
Calculate sum of payments in each method;
GROUP_CONCAT payment methods and sums;
Unfortunately, SUM() doesn't work with GROUP_CONCAT. Some solutions I found on this site suggest using CONCAT, but that doesn't produce the list I need. Other solutions suggest using CAST(), but maybe I do something wrong because it doesn't work too. This is the closest query I wrote, which returns each company, and unique list of payment methods used by each company, but doesn't return the sum of payments:
SELECT *,
(some other sub-queries I need...),
(SELECT GROUP_CONCAT(DISTINCT(mpt_payment_methods.payment_method_title))
FROM mpt_payments
JOIN mpt_payment_methods
ON mpt_payments.payment_method_id=mpt_payment_methods.payment_method_id
WHERE mpt_payments.company_id=mpt_companies.company_id
ORDER BY mpt_payment_methods.payment_method_title) AS payment_data
FROM mpt_companies
Then I tried:
SELECT *,
(some other sub-queries I need...),
(SELECT GROUP_CONCAT(DISTINCT(mpt_payment_methods.payment_method_title), ':', CAST(SUM(mpt_payments.payment_amount) AS CHAR))
FROM mpt_payments
JOIN mpt_payment_methods
ON mpt_payments.payment_method_id=mpt_payment_methods.payment_method_id
WHERE mpt_payments.company_id=mpt_companies.company_id
ORDER BY mpt_payment_methods.payment_method_title) AS payment_data
FROM mpt_companies
...and many other variations, but all of them either returned query errors, either didn't return/format data I need.
The closest answer I could find was MySQL one to many relationship: GROUP_CONCAT or JOIN or both? but after spending 2 hours re-writing the provided query to work with my data, I couldn't do it.
Could anyone give me a suggestion, please?
You can do that by aggregating twice. First for the sum of payments per method and company and then to concatenate the sums for each company.
SELECT x.company_id,
x.company_title,
group_concat(payment_amount_and_method) payment_data
FROM (SELECT c.company_id,
c.company_title,
concat(pm.payment_method_title, ':', sum(p.payment_amount)) payment_amount_and_method
FROM mpt_companies c
INNER JOIN mpt_payments p
ON p.company_id = c.company_id
INNER JOIN mpt_payment_methods pm
ON pm.payment_method_id = p.payment_method_id
GROUP BY c.company_id,
c.company_title,
pm.payment_method_id,
pm.payment_method_title) x
GROUP BY x.company_id,
x.company_title;
db<>fiddle
Here you go
SELECT company_id,
company_title,
GROUP_CONCAT(
CONCAT(payment_method_title, ':', payment_amount)
) AS payment_data
FROM (
SELECT c.company_id, c.company_title, pm.payment_method_id, pm.payment_method_title, SUM(p.payment_amount) AS payment_amount
FROM mpt_payments p
JOIN mpt_companies c ON p.company_id = c.company_id
JOIN mpt_payment_methods pm ON pm.payment_method_id = p.payment_method_id
GROUP BY p.company_id, p.payment_method_id
) distinct_company_payments
GROUP BY distinct_company_payments.company_id
;
class_table
+----+-------+--------------+
| id |teac_id| student_id |
+----+-------+--------------+
| 1 | 1 | 1,2,3,4 |
+----+-------+--------------+
student_mark
+----+----------+--------+
| id |student_id| marks |
+----+----------+--------+
| 1 | 1 | 12 |
+----+----------+--------+
| 2 | 2 | 80 |
+----+----------+--------+
| 3 | 3 | 20 |
+----+----------+--------+
I have these two tables and i want to calculate the total marks of student and my sql is:
SELECT SUM(`marks`)
FROM `student_mark`
WHERE `student_id` IN
(SELECT `student_id` FROM `class_table` WHERE `teac_id` = '1')
But this will return null, please help!!
DB fiddle
Firstly, you should never store comma separated data in your column. You should really normalize your data. So basically, you could have a many-to-many table mapping teacher_to_student, which will have teac_id and student_id columns.
In this particular case, you can utilize Find_in_set() function.
From your current query, it seems that you are trying to getting total marks for a teacher (summing up marks of all his/her students).
Try:
SELECT SUM(sm.`marks`)
FROM `student_mark` AS sm
JOIN `class_table` AS ct
ON FIND_IN_SET(sm.`student_id`, ct.`student_id`) > 0
WHERE ct.`teac_id` = '1'
In case, you want to get total marks per student, you would need to add a Group By. The query would look like:
SELECT sm.`student_id`,
SUM(sm.`marks`)
FROM `student_mark` AS sm
JOIN `class_table` AS ct
ON FIND_IN_SET(sm.`student_id`, ct.`student_id`) > 0
WHERE ct.`teac_id` = '1'
GROUP BY sm.`student_id`
Just in case you want to know why, The reason it returned null is because the subquery returned as '1,2,3,4' as a whole. What you need is to make it returned 1,2,3,4 separately.
What your query returned
SELECT SUM(`marks`)
FROM `student_mark`
WHERE `student_id` IN ('1,2,3,4')
What you expect is
SELECT SUM(`marks`)
FROM `student_mark`
WHERE `student_id` IN (1,2,3,4)
The best way is it normalize as #madhur said. In your case you need to make the teacher and student as one to many link
+----+-------+--------------+
| id |teac_id| student_id |
+----+-------+--------------+
| 1 | 1 | 1 |
+----+-------+--------------+
| 2 | 1 | 2 |
+----+-------+--------------+
| 3 | 1 | 3 |
+----+-------+--------------+
| 4 | 1 | 4 |
+----+-------+--------------+
If you want to filter your table based on a comma separated list with ID, my approach is to
append extra commas at the beginning and at the end of a list as well as at the beginning and at the end of an ID, eg.
1 becomes ,1, and list would become ,1,2,3,4,. The reason for that is to avoid ambigious matches like 1 matches 21 or 12 in a list.
Also, EXISTS is well-suited in that situation, which together with INSTR function should work:
SELECT SUM(`marks`)
FROM `student_mark` sm
WHERE EXISTS(SELECT 1 FROM `class_table`
WHERE `teac_id` = '1' AND
INSTR(CONCAT(',', student_id, ','), CONCAT(',', sm.student_id, ',')) > 0)
Demo
BUT you shouldn't store related IDs in one cell as comma separated list - it should be foreign key column to form proper relation. Joins would become trivial then.
I need to create a number adding all the values i can find in the db related to a specific customer.
Ex.
| Cust. | Value |
| 1 | 3 |
| 2 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 5 |
The result i want is : Customer #1 = 4, Customer #2 = 2; Customer #3 = 5.
There is a way to do that right into the mysql query?
Try Below query.
Select CONCAT('Customer #' , cust) as customer , sum(Value)
FROM customer_table
Group By cust
You want to SUM the values with a specific GROUP BY clause. Think of the GROUP BY as dividing rows into buckets and the SUM as aggregating the contents of those buckets into something useful.
Something like:
SELECT SUM(Value) FROM table GROUP BY Cust
So I have this table, three of the columns are:
So I wanna get the id_keg, and the persen (SELECT DISTINCT).
The persen is the average of persen with the same id_keg.
The result will be pretty much like this:
----------------------
| id_keg | persen |
----------------------
| 202 | 98.00 |
| 101 | 98.89 |
| 102 | 96.43 |
----------------------
I can't seem to find the way to do this. I want to get id_keg and the persen.
I only understand this and I know this won't do:
SELECT AVG (persen) WHERE id_keg=202 FROM laporan.
You need group by while using the aggregate function avg
select
id_keg, avg(persen) as persen
from laporan group by id_keg
You need a Group By clause:
SELECT id_keg, AVG(persen) FROM laporan GROUP BY id_keg
I have a table like this:
Table: p
+----------------+
| id | w_id |
+---------+------+
| 5 | 8 |
| 5 | 10 |
| 5 | 8 |
| 5 | 10 |
| 5 | 8 |
| 6 | 5 |
| 6 | 8 |
| 6 | 10 |
| 6 | 10 |
| 7 | 8 |
| 7 | 10 |
+----------------+
What is the best SQL to get the following result? :
+-----------------------------+
| id | most_used_w_id |
+---------+-------------------+
| 5 | 8 |
| 6 | 10 |
| 7 | 8 |
+-----------------------------+
In other words, to get, per id, the most frequent related w_id.
Note that on the example above, id 7 is related to 8 once and to 10 once.
So, either (7, 8) or (7, 10) will do as result. If it is not possible to
pick up one, then both (7, 8) and (7, 10) on result set will be ok.
I have come up with something like:
select counters2.p_id as id, counters2.w_id as most_used_w_id
from (
select p.id as p_id,
w_id,
count(w_id) as count_of_w_ids
from p
group by id, w_id
) as counters2
join (
select p_id, max(count_of_w_ids) as max_counter_for_w_ids
from (
select p.id as p_id,
w_id,
count(w_id) as count_of_w_ids
from p
group by id, w_id
) as counters
group by p_id
) as p_max
on p_max.p_id = counters2.p_id
and p_max.max_counter_for_w_ids = counters2.count_of_w_ids
;
but I am not sure at all whether this is the best way to do it. And I had to repeat the same sub-query two times.
Any better solution?
Try to use User defined variables
select id,w_id
FROM
( select T.*,
if(#id<>id,1,0) as row,
#id:=id FROM
(
select id,W_id, Count(*) as cnt FROM p Group by ID,W_id
) as T,(SELECT #id:=0) as T1
ORDER BY id,cnt DESC
) as T2
WHERE Row=1
SQLFiddle demo
Formal SQL
In fact - your solution is correct in terms of normal SQL. Why? Because you have to stick with joining values from original data to grouped data. Thus, your query can not be simplified. MySQL allows to mix non-group columns and group function, but that's totally unreliable, so I will not recommend you to rely on that effect.
MySQL
Since you're using MySQL, you can use variables. I'm not a big fan of them, but for your case they may be used to simplify things:
SELECT
c.*,
IF(#id!=id, #i:=1, #i:=#i+1) AS num,
#id:=id AS gid
FROM
(SELECT id, w_id, COUNT(w_id) AS w_count
FROM t
GROUP BY id, w_id
ORDER BY id DESC, w_count DESC) AS c
CROSS JOIN (SELECT #i:=-1, #id:=-1) AS init
HAVING
num=1;
So for your data result will look like:
+------+------+---------+------+------+
| id | w_id | w_count | num | gid |
+------+------+---------+------+------+
| 7 | 8 | 1 | 1 | 7 |
| 6 | 10 | 2 | 1 | 6 |
| 5 | 8 | 3 | 1 | 5 |
+------+------+---------+------+------+
Thus, you've found your id and corresponding w_id. The idea is - to count rows and enumerate them, paying attention to the fact, that we're ordering them in subquery. So we need only first row (because it will represent data with highest count).
This may be replaced with single GROUP BY id - but, again, server is free to choose any row in that case (it will work because it will take first row, but documentation says nothing about that for common case).
One little nice thing about this is - you can select, for example, 2-nd by frequency or 3-rd, it's very flexible.
Performance
To increase performance, you can create index on (id, w_id) - obviously, it will be used for ordering and grouping records. But variables and HAVING, however, will produce line-by-line scan for set, derived by internal GROUP BY. It isn't such bad as it was with full scan of original data, but still it isn't good thing about doing this with variables. On the other hand, doing that with JOIN & subquery like in your query won't be much different, because of creating temporery table for subquery result set too.
But to be certain, you'll have to test. And keep in mind - you already have valid solution, which, by the way, isn't bound to DBMS-specific stuff and is good in terms of common SQL.
Try this query
select p_id, ccc , w_id from
(
select p.id as p_id,
w_id, count(w_id) ccc
from p
group by id,w_id order by id,ccc desc) xxx
group by p_id having max(ccc)
here is the sqlfidddle link
You can also use this code if you do not want to rely on the first record of non-grouping columns
select p_id, ccc , w_id from
(
select p.id as p_id,
w_id, count(w_id) ccc
from p
group by id,w_id order by id,ccc desc) xxx
group by p_id having ccc=max(ccc);