I have three tables STUDENTS, SUBJECTS, RANK ,with data as -
1) STUDENTS [NAME(Primary)]
NAME
--------
Alex
Greg
2) SUBJECTS [ID(Primary)]:
ID
--------
100
101
102
3) RANK [SEQ(Primary), NAME, ID, RANK]
SEQ NAME ID RANK
------ ------- ------ ------
1 Alex 100 A
2 Greg 100 A
3 Greg 101 B
I want to create a view that should display data as
NAME ID RANK
------- ------ ------
Alex 100 A
Alex 101 Z
Alex 102 Z
Greg 100 A
Greg 101 B
Greg 102 Z
So, for every student and for every subject, the View should display the RANK if present in RANK table, else replace the NULL with 'Z'.
I'm a newbie to SQL. So any help in forming the query would be deeply appreciated!
cross join student and subject then left outer join the result with rank to get ranks for all (student, subject) combination. selecting column with NVL OR COALESCE will replace NULL with 'z'.
SELECT st.name,
su.id,
NVL(ra.rank,'Z') Rank, --COALESCE(ra.rank,'Z') Rank
FROM student st
CROSS JOIN subject su
LEFT OUTER JOIN rank ra
ON ra.name = st.name
AND ra.id = su.id
ORDER BY st.name,su.id
Note : ORDER BY can be removed from above query if you don't need.
fiddle
SELECT r.NAME, r.ID, NVL(r.RANK, 'Z')
FROM RANK r, studendts st, SUBJECTS su
WHERE st. NAME = r. NAME
AND su.ID = r.ID
ORDER BY 1,2,3
Related
Say for example.
I have three separate tables:
course Table which has CourseId, StudentIds etc
student which of course contains student data and StudentName
score table
I only want one column from each table and fuse them into one.
CourseId StudentName Scores
---------- ------------- ----------
1 Gashio 10
1 Gashio 20
1 Lee 35
1 Lee 40
1 Edith 5
2 Lana 3
2 Reisha 50
For every Course there's multiple students, and for every Scores there's multiple scores they get from the course for a month.
I wanted something like this as a result:
CourseId StudentName Scores
--------- ------------- -------------
1 Gashio 10|20
1 Lee 35|40
1 Edith 5
2 Lana 3
2 Reisha 50
Since the scores return multiple values, I wanted it to become one column separated by a delimeter.
I'm not sure if this is where I should be using STRING_AGG?
You need STRING_AGG and GROUP BY
SELECT course.CourseId,
student.StudentName,
STRING_AGG(Scores, ,'|') AS Scores
FROM course INNER JOIN
student ON student.StudentId = course.StudentId INNER JOIN
score ON score.studentId = student.StudentId
GROUP BY cource.CourseId,
student.StudentName
use string_agg() with delimeter
select CourseId,StudentName,string_agg(Scores,'|') as scores
from tablename
group by CourseId,StudentName
I have two tables, emp and location. I need to fetch the records for all the matching eid s' of emp table based on location type.
If the location type=2 then we need to fetch the city associated with it.
If we don't have type=2 record we need to fetch type=1 associated city for the matching eid.
My case statement works fine until there are two records for the eid of both type 1 and type 2. But I need to fetch only type 2 in this case
select case when a.type=2 then a.city
When a.type=1 then a.city
Else '0' End As City
From location a
Join emp r
On a.eid=r.eid
emp table
eid ename
1 james
2 mark
3 kristie
4 john
5 allen
location table
city eid type
athens 1 2
melbourne 2 1
london 2 2
newyork 3 1
output:
eid ename city type
1 james athens 2
2 mark london 2
3 kristie newyork 1
I think the most direct way to represent what you're asking for is:
select coalesce(l2.city, l1.city, '0') as city
From emp r
left join location l1
on l1.eid = r.eid
and l1.type=1
left join location l2
on l2.eid = r.eid
and l2.type=2
The subquery-based solution proposed by Jeremy Real may also work, but it assumes that 1 and 2 are they only values in the table for location.type (and I just don't find it to be as intuitive).
Try this:
select a.eid
,r.ename
,case when a.type=2 then b.city
when a.type=1 then b.city
else '0' End As City
from (
select a.eid, max(a.type) as type
From location a
group by a.eid
) a
right outer join location b
on a.eid = b.eid and a.type=b.type
inner join emp r
on b.eid=r.eid
You want to rank your cities. Use ROW_NUMBER to do that:
select e.eid, e.name, l.city, l.type
from emp e
join
(
select
city, eid, type,
row_number() over (partition by eid order by type desc) as rn
from location
) l on l.eid = e.eid and l.rn = 1;
rn is 1 for the better city per eid (where "better" is the one with the higher type).
I have 2 tables with one having a reference to the first by id
first table for example is customer having the fields
id firstname lastname
------ --------- ---------
1 john smith
2 jessica james
the second table for example is product having the fields
id customer_id product descr
------- ----------- --------- ------
1 1 ts Shirt
2 1 ti Tie
3 2 sk skrit
I need a query that will output the following
customer.firstname customer.lastname product_and_desc
------------------ ------------------ ---------------------
john smith ts-Shirt , ti-Tie
jessica james sk-skirt
with the product rows variable for each customer.
I appreciate you help :)
thanks,
You can use list_agg(). In your case:
select c.firstname, c.lastname,
list_agg(p.product||'-'||p.desc, ' , ') within group (order by p.id) as product_and_desc
from customer c join
product p
on c.id = p.customer_id
group by c.firstname, c.lastname;
I would suggest, though, that the second argument to list_agg() be ', ' rather than ' , '. The space before the comma looks a bit unusual.
select first_name,last_name,wm_concat(product||'-'||descr) as product_and_descr
from tbl1 ,tbl2 where tbl1.id=tbl2.customer_id
group by first_name,last_name;
Student
student_id FirstName LastName
---------------------------------------------------
1 Joe Bloggs
2 Alan Day
3 David Johnson
Student_Course
course_id student_id courseName
---------------------------------------------------
1 1 Computer Science
2 1 David Beckham Studies
3 1 Geography
1 3 Computer Science
3 3 Geography
Student_clubs
club_id student_id club_name club_count
---------------------------------------------------
1 1 Footbal 10
2 1 Rugby 10
3 1 Syncronized Swimming 10
4 3 Tennis 15
In the above example, student with id = 1 takes 3 course and is part of 3 clubs.
If i was to find out which courses a student is involved in or which club the student is part of i can do it but i will need to run two queries. Is it possible to run a single query against the
tables listed above so that the results come out like this:
Output
student_id FirstName Student_associated_courses Student_associated_clubs
---------------------------------------------------------------------------
1 Joe 1,2,3 Football, Rugby, Syncronized swimming
3 David 1,3 Tennis
Is it possible to get the above output with just one query? I am using JDBC to get the data so i am trying to see if i can avoid multiple trips to get the necessary data.
use GROUP_CONCAT with DISTINCT in MySQL
SELECT a.student_ID, a.firstname,
GROUP_CONCAT(DISTINCT b.course_ID),
GROUP_CONCAT(DISTINCT c.club_name)
FROM student a
INNER JOIN student_Course b
ON a.student_id = b.student_ID
INNER JOIN student_clubs c
ON a.student_ID = c.student_ID
GROUP BY a.student_ID, a.firstname
See SQLFiddle Demo
Try it like this:
SELECT *
FROM Student s JOIN
(SELECT sc."student_id", listagg(sc."course_id", ',')within group(ORDER BY sc."course_id")
FROM Student_Course sc
GROUP BY sc."student_id") s_course ON s."student_id"=s_course."student_id"
JOIN (SELECT sl."student_id", listagg(sl."club_name", ',')within GROUP(ORDER BY sl."club_name")
FROM Student_clubs sl
GROUP BY sl."student_id") s_club ON s."student_id"=s_club."student_id"
The "catch" is that LISTAGG doesn't work with DISTINCT keyword
Here is a fiddle
How would I be able to get N results for several groups in
an oracle query.
For example, given the following table:
|--------+------------+------------|
| emp_id | name | occupation |
|--------+------------+------------|
| 1 | John Smith | Accountant |
| 2 | Jane Doe | Engineer |
| 3 | Jack Black | Funnyman |
|--------+------------+------------|
There are many more rows with more occupations. I would like to get
three employees (lets say) from each occupation.
Is there a way to do this without using a subquery?
I don't have an oracle instance handy right now so I have not tested this:
select *
from (select emp_id, name, occupation,
rank() over ( partition by occupation order by emp_id) rank
from employee)
where rank <= 3
Here is a link on how rank works: http://www.psoug.org/reference/rank.html
This produces what you want, and it uses no vendor-specific SQL features like TOP N or RANK().
SELECT MAX(e.name) AS name, MAX(e.occupation) AS occupation
FROM emp e
LEFT OUTER JOIN emp e2
ON (e.occupation = e2.occupation AND e.emp_id <= e2.emp_id)
GROUP BY e.emp_id
HAVING COUNT(*) <= 3
ORDER BY occupation;
In this example it gives the three employees with the lowest emp_id values per occupation. You can change the attribute used in the inequality comparison, to make it give the top employees by name, or whatever.
Add RowNum to rank :
select * from
(select emp_id, name, occupation,rank() over ( partition by occupation order by emp_id,RowNum) rank
from employee)
where rank <= 3
tested this in SQL Server (and it uses subquery)
select emp_id, name, occupation
from employees t1
where emp_id IN (select top 3 emp_id from employees t2 where t2.occupation = t1.occupation)
just do an ORDER by in the subquery to suit your needs
I'm not sure this is very efficient, but maybe a starting place?
select *
from people p1
join people p2
on p1.occupation = p2.occupation
join people p3
on p1.occupation = p3.occupation
and p2.occupation = p3.occupation
where p1.emp_id != p2.emp_id
and p1.emp_id != p3.emp_id
This should give you rows that contain 3 distinct employees all in the same occupation. Unfortunately, it will give you ALL combinations of those.
Can anyone pare this down please?