I'm trying to denormalize a result set so that I have one record per ID. This is a list of patients with multiple comorbidities. The data currently looks like this:
ID Disease
1 Asthma
1 Cancer
1 Anemia
2 Asthma
2 HBP
And I need it to look like this:
ID Disease1 Disease2 Disease3
1 Asthma Cancer Anemia
2 Asthma HBP <NULL or Blank>
I researched Pivot, but all of the examples I saw used aggregate functions which wouldn't apply.
I have added the row_number function and tried self joins like the following:
case when rownum = 1 then Disease else NULL end Disease1,
case when rownum = 2 then Disease else NULL end Disease2,
case when rownum = 3 then Disease else NULL end Disease3
However, this produces the following:
ID Disease1 Disease2 Disease3
1 Asthma NULL NULL
1 NULL Cancer NULL
1 NULL NULL Anemia
2 Asthma NULL NULL
2 NULL HBP NULL
Any suggestions would be greatly appreciated. I would really like to find a way to accomplish this without having a monstrous block of code (which is what I ended up with when trying to do it). Thanks!
You can use MAX to compact the rows:
select
id,
max(case when rownum = 1 then Disease end) Disease1,
max(case when rownum = 2 then Disease end) Disease2,
max(case when rownum = 3 then Disease end) Disease3
from (
select
id,
disease,
rownum = ROW_NUMBER() OVER (partition by id order by id)
from your_table
) sub
group by id
Sample SQL Fiddle
Related
Here's what I am currently getting from my query:
row_no
prospect
hot
contract
1
null
Joe
null
1
John
null
null
1
null
null
Sam
I Am trying to get:
row_no
prospect
hot
contract
1
John
Joe
Sam
I cannot use concate because I still need separate columns
Here's what I have so far...
https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=e7aab240b40e40955bac44f616d7f3d7
Please note: Ultimately, there will be 7 columns, but a varying amount of rows (ie. the prospect column may have 20 records, where the contract column may only have four or five.
You can do it with conditional aggregation:
WITH CTE_tbl AS
(
SELECT lead_type,firstname, last_date,
ROW_NUMBER() OVER(PARTITION BY lead_type order by lead_type Desc) as row_no
FROM leads
)
SELECT row_no,
MAX(case when lead_type = 'prospect' then firstname end) prospect,
MAX(case when lead_type = 'hot' then firstname end) hot,
MAX(case when lead_type = 'contract' then firstname end) contract
FROM CTE_tbl
GROUP BY row_no
ORDER BY row_no
See the demo.
Results:
row_no
prospect
hot
contract
1
John
Joe
Sam
2
Mario
Autumn
null
3
Frank
null
null
4
Mary
null
null
5
Steve
null
null
I am trying to understand how this subquery works. The questions are as follows
Mary is a teacher in a middle school and she has a table seat storing students' names and their corresponding seat ids.The column id is continuous increment.
Mary wants to change seats for the adjacent students.
SELECT
(CASE
WHEN MOD(id, 2) != 0 AND counts != id THEN id + 1
WHEN MOD(id, 2) != 0 AND counts = id THEN id
ELSE id - 1
END) AS id,
student
FROM
seat,
(SELECT
COUNT(*) AS counts
FROM
seat) AS seat_counts
ORDER BY id ASC;
I am trying to understand the how the above query works. So in the CASE it checks if the id is odd or even and checks against the count to see if it is the last element. But how does the ORDER BY ASC work? Because for the first time it selects student Dorris and id 2. but then how is id 2 assigned to Abbot. Thanks.
SQL Table
id | student
1 | Abbot
2 | Doris
3 | Emerson
4 | Green
5 | Jeames
The Result will look like
id | student
1 | Dorris
2 | Abbot
3 | Green
4 | Emerson
5 | Jeames
OK what this is doing is the following -- if an id number is odd and it is not the max number then add one to it, otherwise subtract one from it.
It should be clear that would swap all but the last pair.
I think it is badly written I would write it like this:
WITH student_count(max) as
(
SELECT COUNT(*) FROM seat
)
SELECT
CASE
WHEN student_count.max != id AND MOD(id, 2) != 0 THEN id + 1
WHEN student_count.max != id AND MOD(id, 2) = 0 THEN id - 1
ELSE id
END AS id,
student
FROM seat
CROSS JOIN student_count
ORDER BY id ASC;
I would recommend you to check the results by removing ORDER BY statement. When you remove ORDER BY statement, result will be:
2 Abbot
1 Doris
4 Emerson
3 Green
5 Jeames
Which is completely right for your case. Basically, your query just alters id's values based on the CASE statement. When you add ORDER BY id ASC statement it just orders the result above.
select name,
case when mod(seat_id,2) = 1 and seat_id <> (select max(seat_id) from students) then seat_id + 1
when mod(seat_id,2)= 0 then seat_id - 1
when mod(seat_id,2) = 1 and seat_id = (select max(seat_id) from students) then seat_id
end swap
from students
SELECT
(CASE
WHEN MOD(id, 2) != 0 AND counts != id THEN id + 1
WHEN MOD(id, 2) != 0 AND counts = id THEN id
ELSE id - 1
END) AS id,
student
FROM
seat,
(SELECT
COUNT(*) AS counts
FROM
seat) AS seat_counts
ORDER BY id ASC;
I need to group the table during my query, and up until know I was doing that after querying - with the code as my group is quite complicated. But with the new data it appears to take minutes, and I'm thinking is there better way.
My current query results in this:
FKId | Name | A | B | C
1 Alpha 2 3 2
1 Beta 2 5 7
2 Alpha 8 1 10
2 Beta 7 -5 6
2 Gamma 1 2 3
And I convert it to this:
FKId | Alpha[A] | Alpha[B] | Alpha[C] | Beta[A] | Beta[B] | Beta[C] | Gamma[A] | Gamma[B] | Gamma[C]
1 2 3 2 2 5 7
2 8 1 10 7 -5 6 1 2 3
Is it possible to do with SQL? (and I assume it should be much faster than if I do this with code)
The names can be anything
I have very big number of colums A, B, C (like 20 - 30). The number of result columns can easily go to thousands as average project has about 100 names.
I have like 10-20 columns that I should group by, but doing a single group by FKId is fine - these columns are the same.
We use different SQL DBs, so I cannot use specific functions like PIVOT. I know that we used MySQL, MsSQL and SQLite a lot
We use NHibernate if it makes any difference.
I would also honor the solution done for MySQL if specific functions are used. We use it in 80% and it will already greatly improve the average performance if I could do that at least for MySQL.
Basically, you want to transpose the data. Here is what you can try. It should work across all databases but you need to know the columns A, B, C, etc beforehand:
create table my_table (
fkid integer,
name varchar(10),
a integer,
b integer,
c integer
);
insert into my_table values(1,'alpha',2,3,2)
,(1,'beta',2,5,7)
,(2,'alpha',8,1,10)
,(2,'beta',7,-5,6)
,(2,'gamma',1,2,3);
select fkid
, max(case when name = 'alpha' then a else null end) as alphaa
, max(case when name = 'alpha' then b else null end) as alphab
, max(case when name = 'alpha' then c else null end) as alphac
, max(case when name = 'beta' then a else null end) as betaa
, max(case when name = 'beta' then b else null end) as betab
, max(case when name = 'beta' then c else null end) as betac
, max(case when name = 'gamma' then a else null end) as gammaa
, max(case when name = 'gamma' then b else null end) as gammab
, max(case when name = 'gamma' then c else null end) as gammac
from my_table
group by fkid;
I have a table where there are columns students and grade obtained(A-F). A student can appear for test more than once. Sometimes students register but do not appear for test so the grade is not entered but student record entry is made.
I want to get best grade of each student. When I do min(grade) if there is any record with null, null gets selected instead of 'A-F' which indicate proper results. I want to get min of grade if grade exists or null if there are no grades.
SELECT `name`,min(grade) FROM `scores` group by `name`
Id | Name | Grade
1 | 1 | B
2 | 1 |
3 | 1 | A
4 | 2 | C
5 | 2 | D
For name 1 it is fetching second record not the third one having 'A'.
As per the conversations in the comments, the easiest solution may be to convert your empty strings to null, and let the builtin min function do the heavy lifting:
ALTER TABLE scores MODIFY grade VARCHAR(1) NULL;
UPDATE scores
SET grade = null
WHERE grade = '';
SELECT name, MIN(grade)
FROM scores
GROUP BY name
If this is not possible, a dirty trick you could use is to have a case expression convert the empty string to a something you know will come after F:
SELECT name,
MIN(CASE grade WHEN '' THEN 'DID NOT PARTICIPATE' ELSE grade END)
FROM scores
GROUP BY name
And if you really need the empty string back, you can have another case expression around the min:
SELECT name, CASE best_grade WHEN 'HHH' THEN '' ELSE best_grade END
FROM (SELECT name,
MIN(CASE grade WHEN '' THEN 'HHH' ELSE grade END) AS
best_grade
FROM scores
GROUP BY name) t
Change your query slightly to -
SELECT `name`,min(grade) FROM `scores` WHERE grade <> "" group by `name`
If the name has a grade/s assigned to it then the lowest will be returned else the resultset will be null
I don't know how to title this Q.
I got a table in my DB that's looking like this:
[id][name][type]
1-John-2
2-Jack-3
3-Liam-1
4-Kim-1
5-Michael-3
And many more
I would like to make a list where it's grouped by type,
but where type 1 and 2 is one group, like this:
[Type 1 and 2]
1 - John
3 - Liam
4 - Kim
[Type 3]
2 - Jack
Is it possible to group like that in MySQL?
Yes you can use case
select *,
case when `type` =2 then 1 else `type` end new_type
from t
order by `type` ;
With aggregate fucntions
select count(*)
,case when `type` =2 then 1 else `type` end new_type
from t
group by new_type
Demo