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.
Related
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
I have inherited a table where one column is a comma-separated list of primary keys for a different table:
id | other_ids | value
---|-----------|-------
1 | a,b,c | 100
2 | d,e | 200
3 | f,g | 3000
I would like to convert this table to one where each other_id gets a column of its own:
id | other_id
---|---------
1 | a
1 | b
1 | c
2 | d
2 | e
3 | f
3 | g
However, I cannot think of a way to do this?
The table is > 10 GB in size, so I would like to do this inside the database, if possible.
first time post, please be kind.
Try this
select id,SUBSTRING_INDEX(other_ids,',',1) as other_id from reverseconcat
UNION
select id,SUBSTRING_INDEX(SUBSTRING_INDEX(other_ids,',',2),',',-1) as other_id from reverseconcat
UNION
select id,SUBSTRING_INDEX(SUBSTRING_INDEX(other_ids,',',3),',',-1) as other_id from reverseconcat
order by id
Although I cant really take any credit. Found this on http://www.programering.com/a/MzMyUzNwATg.html
Unsure how you will go on a huge dataset. Also you will need to add more unions if the other_ids are > 3
If you have the other table, then you can use a join and find_in_set():
select t.id, ot.pk as other_id
from t join
othertable ot
on find_in_set(ot.pk, t.other_ids) > 0;
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
Had a good read through similar topics but I can't quite a) find one to match my scenario, or b) understand others enough to fit / tailor / tweek to my situation.
I have a table, the important fields being;
+------+------+--------+--------+
| ID | Name | Price |Status |
+------+------+--------+--------+
| 1 | Fred | 4.50 | |
| 2 | Fred | 4.50 | |
| 3 | Fred | 5.00 | |
| 4 | John | 7.20 | |
| 5 | John | 7.20 | |
| 6 | John | 7.20 | |
| 7 | Max | 2.38 | |
| 8 | Max | 2.38 | |
| 9 | Sam | 21.00 | |
+------+------+--------+--------+
ID is an auto-incrementing value as records get added throughout the day.
NAME is a Primary Key field, which can repeat 1 to 3 times in the whole table.
Each NAME will have a PRICE value, which may or may not be the same per NAME.
There is also a STATUS field that need to be populated based on the following, which is actually the part I am stuck on.
Status = 'Y' if each DISTINCT name has only one price attached to it.
Status = 'N' if each DISTINCT name has multiple prices attached to it.
Using the table above, ID's 1, 2 and 3 should be 'N', whilst 4, 5, 6, 7, 8 and 9 should be 'Y'.
I think this may well involve some form of combination of JOINs, GROUPs, and DISTINCTs but I am at a loss on how to put that into the right order for SQL.
In order to get the count of distinct Price values per name, we must use a GROUP BY on the Name field, but since you also want to display all names ungrouped but with an additional Status field, we must first create a subselect in the FROM clause which groups by the name and determines whether the name has multiple price values or not.
When we GROUP BY Name in the subselect, COUNT(DISTINCT price) will count the number of distinct price values for each particular name. Without the DISTINCT keyword, it would simply count the number of rows where price is not null.
In conjunction with that, we use a CASE expression to insert N into the Status column if there is more than one distinct Price value for the particular name, otherwise, it will insert Y.
The subselect only returns one row per Name, so to get all names ungrouped, we join that subselect to the main table on the condition that the subselect's Name = the main table's Name:
SELECT
b.ID,
b.Name,
b.Price,
a.Status
FROM
(
SELECT Name, CASE WHEN COUNT(DISTINCT Price) > 1 THEN 'N' ELSE 'Y' END AS Status
FROM tbl
GROUP BY Name
) a
INNER JOIN
tbl b ON a.Name = b.Name
Edit: In order to facilitate an update, you can incorporate this query using JOINs in the UPDATE like so:
UPDATE
tbl a
INNER JOIN
(
SELECT Name, CASE WHEN COUNT(DISTINCT Price) > 1 THEN 'N' ELSE 'Y' END AS Status
FROM tbl
GROUP BY Name
) b ON a.Name = b.Name
SET
a.Status = b.Status
Assuming you have an unfilled Status column in your table.
If you want to update the status column, you could do:
UPDATE mytable s
SET status = (
SELECT IF(COUNT(DISTINCT price)=1, 'Y', 'N') c
FROM (
SELECT *
FROM mytable
) s1
WHERE s1.name = s.name
GROUP BY name
);
Technically, it should not be necessary to have this:
FROM (
SELECT *
FROM mytable
) s1
but there is a mysql limitation that prevents you to select from the table you're updating. By wrapping it in parenthesis, we force mysql to create a temporary table and then it suddenly is possible.
Alright so I have a table, in this table are two columns with ID's. I want to make one of the columns distinct, and once it is distinct to select all of those from the second column of a certain ID.
Originally I tried:
select distinct inp_kll_id from kb3_inv_plt where inp_plt_id = 581;
However this does the where clause first, and then returns distinct values.
Alternatively:
select * from (select distinct(inp_kll_id) from kb3_inv_plt) as inp_kll_id where inp_plt_id = 581;
However this cannot find the column inp_plt_id because distinct only returns the column, not the whole table.
Any suggestions?
Edit:
Each kll_id may have one or more plt_id. I would like unique kll_id's for a certain kb3_inv_plt id.
| inp_kll_id | inp_plt_id |
| 1941 | 41383 |
| 1942 | 41276 |
| 1942 | 38005 |
| 1942 | 39052 |
| 1942 | 40611 |
| 1943 | 5868 |
| 1943 | 4914 |
| 1943 | 39511 |
| 1944 | 39511 |
| 1944 | 41276 |
| 1944 | 40593 |
| 1944 | 26555 |
If you do mean, by "make distinct", "pick only inp_kll_ids that happen just once" (not the SQL semantics for Distinct), this should work:
select inp_kll_id
from kb3_inv_plt
group by inp_kll_id
having count(*)=1 and inp_plt_id = 581;
Get all the distinct first (alias 'a' in my following example) and then join it back to the table with the specified criteria (alias 'b' in my following example).
SELECT *
FROM (
SELECT
DISTINCT inp_kll_id
FROM kb3_inv_plt
) a
LEFT JOIN kb3_inv_plt b
ON a.inp_kll_id = b.inp_kll_id
WHERE b.inp_plt_id = 581
in this table are two columns with
ID's. I want to make one of the
columns distinct, and once it is
distinct to select all of those from
the second column of a certain ID.
SELECT distinct tableX.ID2
FROM tableX
WHERE tableX.ID1 = 581
I think your understanding of distinct may be different from how it works. This will indeed apply the where clause first, and then get a distinct list of unique entries of tableX.ID2, which is exactly what you ask for in the first part of your question.
By making a row distinct, you're ensuring no other rows are exactly the same. You aren't making a column distinct. Let's say your table has this data:
ID1 ID2
10 4
10 3
10 7
4 6
When you select distinct ID1,ID2 - you get the same as select * because the rows are already distinct.
Can you add information to clear up what you are trying to do?