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
Related
I have the below tables:
Corporate table:
CorporateId DirectorId ManagerId SalesId
1 1 1 1
2 2 2 3
3 3 4 5
Employee table:
EmployeeId FirstName LastName
1 Tim Sarah
2 Tom Paulsen
3 Tam Margo
4 Eli Lot
5 Ziva Lit
I want to display, for one corporate,the names of the Director, Manager and Sales in rows. Example with corporate 3:
EmployeeId FirstName LastName
3 Tam Margo
4 Eli Lot
5 Ziva Lit
How can I do that? I know how to display rows as columns using pivot, but unsure if pivot can be used here also.
Any help please?
You may join the two tables as the following:
SELECT E.EmployeeId, E.FirstName, E.LastName
FROM Employee E JOIN Corporate C
ON E.EmployeeID IN (C.DirectorId ,C.ManagerId ,C.SalesId)
WHERE C.CorporateId=3
See a demo.
You can first un-pivot your rows into columns by using cross apply, after which you simply join the pivoted rows to your employee table:
select e.*
from corporate c
cross apply (
select EmployeeId from (
values (Directorid), (ManagerId), (SalesId)
)r(EmployeeId)
)r
join employee e on e.EmployeeId = r.EmployeeId
where c.CorporateId = 3;
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 a requirement in such a way that it should join two tables with more than 100k records in one table and just 5 records in another table as shown below
Employee Dept Result
id Name deptid deptid Name Name deptid Name
1 Jane 1 1 Science Jane 1 Science
2 Jack 2 2 Maths Dane 1 Science
3 Dane 1 3 Biology Jack 2 Maths
4 Drack 3 4 Social Drack 3 Biology
5 Drim 5 Zoology Kery 4 Social
6 Drum 5 Drum 5 Zoology
7 Krack
8 Kery 4
.
.
100k
Which join need to be used to get the query in an better way to perform to get the result as shown.
I just want the query to join with other table from employee table only which has dept which i thought of below query but wanted to know is there any better way to do it.
Select e.name,d.deptid,d.Name from
(Select deptid,Name from Employee where deptid IS NOT NULL) A
and dept d where A.deptid=d.deptid;
Firstly not sure why you are performing your query the way you are. Should be more like
SELECT A.name, D.deptid,D.Name
FROM Employee A
INNER JOIN dept D
ON A.deptid = D.deptid
No need of the IS NOT NULL statement.
If this is a ONE TIME or OCCASIONAL thing and performance is key (not a permanent query in your DB) you can leave out the join altogether and do it using CASE:
SELECT
A.name, A.deptid,
CASE
WHEN A.deptid = 1 THEN "Science"
WHEN A.deptid = 2 THEN "Maths"
...[etc for the other 3 departments]...
END as Name
FROM Employee A
If this is to be permanent and performance is key, simply try applying an INDEX on the foreign key deptid in the Employee table and use my first query above.
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
If I have a table...
ID Name Manager
0 Joe Sue
1 Jake Tom
0 Joe Tom
2 Larry Red
2 Larry Paul
1 Jake Paul
I want the output to be....
ID Name Manager1 Manager2
0 Joe Sue Tom
1 Jake Tom Paul
2 Larry Red Paul
Thanks...
If I have understood your request properly, yes, something like would produce the results you are looking for.
SELECT
t1.Name Name,
t1.Manager Manager1,
t2.Manager Manager2
FROM
Table t1
inner join Table t2 on t1.Manager = t2.Name
Of course a foreign key back to the index column would be preferential to strong comparisons for performance.
Yeah, if your table was called 'Managers':
SELECT Mgr1.ID,Mgr1.Name,Mgr1.Manager,Mgr2.Manager
FROM Managers AS Mgr1
LEFT JOIN Managers AS Mgr2
ON Mgr1.ID=Mgr2.ID
If your keeping the tables a join would be best.
If you hate joins, you could combine the max and min managers, and even then it would work if there is always 2 managers and they can't have the same name.
The below should work if I remember how to join up 2 queries correctly. but i would advise to see if it is possible to rework your table, have a separate table linking people to each other in a manager employee relation.
SELECT DISTINCT
F.ID, F.Name, S.Manager, F.Manager
FROM
(SELECT
ID, Name, MIN(manager) manager
FROM Managers
GROUP BY ID, Name) F,
(SELECT
ID, Name, MAX(manager) manager
FROM Managers
GROUP BY ID, Name) S
WHERE
F.ID = S.ID
AND S.Manager <> F.Manager
AND F.ID < S.ID