I am using sql-server.I have a table looks like
StudentName Class score
Jim a1 80
Ann a1 83
Bill a2 90
I want to select student whose score is above the average score in his/her class. Here is my code:
Select a.StudentName
From Table a
inner Join Table b
On a.class=b.class
where a.score>(select avg(b.score) From b
group by class);
The inner join method looks odd to me.Is it correct please? Is there any better way to achieve that please?
You're close, but you can limit your sub-query and take out the JOIN:
Select a.StudentName
From Table a
where a.score > (
select avg(b.score) score
From Table b
where b.class = a.class);
How about:
;with ClassAverages as (
select Class, AVG(score) as AVGScore FROM Table GROUP BY Class
)
SELECT StudentName FROM Table student
INNER JOIN ClassAverages ON ClassAverages.Class=student.Class
WHERE student.score>ClassAverages.AVGScore
Related
I have problems displaying columns from two common table expression. I created the first table by querying the student names and their mid-term grades and the other table the student names and their final-term grades.
CREATE TABLE MidTerm AS (SELECT Name, Score
FROM GRADE
WHERE TYPE = ''MidTerm
)
CREATE TABLE FinalTerm AS (SELECT Name, Score
FROM GRADE
WHERE TYPE = 'Final'
)
Both of the created have the same number of columns and the same variables. Now I want to display the Name, Score "MidTerm" and Score "FinalTerm", how can I achieve this? I manage to use UNION at the expense of SELECT * only. If I specify
Midterm table:
Name : Score
A : 50
B : 60
Finalterm table:
Name : Score
A : 70
B : 80
I want to join the CTE tables by displaying
Final Intended Result:
Name : Score "MidTerm" : Score "FinalTerm"
A : 50 : 70
B : 60 : 80
it would say invalid column identifier. How do I solve this?
A simple join will handle this:
SELECT m.NAME AS "Name",
m.SCORE AS "Score MidTerm",
f.SCORE AS "Score FinalTerm"
FROM MIDTERM m
LEFT OUTER JOIN FINALTERM f
ON f.NAME = m.NAME
db<>fiddle here
If you have two tables for midterm and final score as per comment in gordon's answer then just do join and you will get your result like this:
Select m.name,
M.score as midterm_score,
F.score as final_score
From midterm_table m
Join final_table f
on (m.name = f.name);
Cheers!!
I think that you are just looking for conditional aggregation:
select
name,
max(case when score = 'MidTerm' then score end) MidTerm,
max(case when score = 'Final' then score end) Final
from grade
where score in ('MidTerm', 'Final')
group by name
I am baffled. Use conditional aggregation:
SELECT Name,
MAX(CASE WHEN Type = 'MidTerm' THEN Score END) as midterm_score,
MAX(CASE WHEN Type = 'Final' THEN Score END) as final_score,
FROM GRADE
GROUP BY Name;
CTEs do not help with this query at all.
You could also do this using a JOIN:
select m.name, m.score as midterm_score, f.score as final_score
from grade m join
grade f
on m.name = f.name and
m.type = 'midterm' and
f.type = 'final';
Note that this only shows names with both scores.
Add student's id in those tables and use it to join them and gather the columns that you need.
I dont believe that create this two tables is realy a good idea,
but, ok, I don't know the complexity of your calculations to get the score.
anyway, I would suggest to you consider the creation of an view for that instead of create those table.
I think I have end up in a bit of a dead end.
Let's say I have a dataset, which is fairly easy -
person_id and book_id. Which is pretty much factual table that says person X bought books A, B and C.
I know how to find out how many persons have bought Book X and Book Y together.
This is
select a.book_id as B1, b.book_id as B2, count(b.person_id) as
Bought_Together
from dbo.data a
cross join dbo.data b
where a.book_id != b.book_id and a.person_id = b.person_id
group by a.book_id, b.book_id
Yet again this is where my brain decided to shut down. I know that I would probably need to do it so that
count(b.person_id) / all the people that bought book A * 100
but im not entirely sure.
I hope I was clear enough.
EDIT1: I'm using SQL Server 2017 currently, so i think the correct answer is T-SQL?.
In the end the format should be something similliar to this. Also there is no cases where person A could have bought three copies of book X.
Book1 Book2 HowManyPeopleBoughtBook2
1 2 50%
1 3 7%
2 3 15%
2 1 40%
3 1 60%
3 2 20%
EDIT2: Let it be said there is hundreds of thousands of rows in the database. Yes this is bit related to a data science course i am taking - hence huge amounts of data.
You can extend your logic to do this:
select a.book_id as B1, b.book_id as B2,
count(b.book_id) as bought_second_book,
count(b.book_id) * 1.0 / book_cnt as ratio_Bought_Together
from (select a.*, count(*) over (partition by a.book_id) as book_cnt
from dbo.data a
) a left join
dbo.data b
on a.person_id = b.person_id and a.book_id <> b.book_id
group by a.book_id, b.book_id, a.book_cnt;
This assumes that people buy a book only once. If there are duplicates, then count(distinct) would adjust for that.
If you would like to generate all possible combinations of the pairs of books bought together along with the percentage of the persons who bought that combination the following can help
create table data1(book_id int, person_id int)
insert into data1
select *
from (values(1,300)
,(2,300)
,(2,301)
,(1,301)
,(3,301)
)t(book_id,person_id)
with books
as (select distinct book_id
from data1 a
)
,tot_persons
as (select count(distinct person_id) as tot_cnt
from data1
)
,pairs
as (
select a.book_id as col1 /* This block generates all possible pair combinations of books*/
,b.book_id as col2
from books a
join books b
on a.book_id<b.book_id
)
select a.col1,a.col2
,count(b.person_id)*100/(select tot_cnt from tot_persons) as percent_of_persons_buying_both
from pairs a
join data1 b
on a.col1=b.book_id
where exists(select 1
from data1 b1
where b.person_id=b1.person_id
and a.col2=b1.book_id)
group by a.col1,a.col2
On my phone, apologies for typo's
SELECT
SUM(bought_b) * 100.0 / COUNT(*)
FROM
(
SELECT
person_id,
MAX(CASE WHEN book_id = 'A' THEN 1 END) AS bought_a,
MAX(CASE WHEN book_id = 'B' THEN 1 END) AS bought_b
FROM
data
WHERE
book_id IN ('A', 'B')
GROUP BY
person_id
)
person_stats
WHERE
bought_a = 1
On my phone, apologies for typo's
EDIT : just saw that you want all combinations, just just one set combination.
WITH
book AS
(
SELECT DISTINCT book_id FROM data
)
SELECT
book_a_id,
book_b_id,
bought_b * 100.0 / bought_b
FROM
(
SELECT
book_a.book_id AS book_a_id,
book_b.book_id AS book_b_id,
COUNT(DISTINCT data_a.person_id) AS bought_a,
COUNT(DISTINCT data_b.person_id) AS bought_b
FROM
book AS book_a
CROSS JOIN
book AS book_b
INNER JOIN
data AS data_a
ON data_a.book_id = book_a.book_id
LEFT JOIN
data AS data_b
ON data_b.book_id = book_b.book_id
GROUP BY
book_a.book_id,
book_b.book_id
)
stats
Here I have two tables committee_colleges and colleges.
Structure of tables is something like this
committee_colleges
committeeCollegeId collegeId committeeMemberId
1 2 1
2 2 2
3 3 2
I am storing committeeMemberId from committeeMember table.And one college can have multiple committee Members.How can I wite a query to display only the colleges assigned to specific committee Member.
For Example,if committeeMember by id=2 has logged in I want to display colleges by id=2,3.
In college table I have like this,
collegeId typeName
1 AICTE
2 NCTE
3 NTCS
This is Committee Member table
committeeMemberId name
1 xyz
2 abc
Now I am writing something like this,but i know its wrong because I dont know how to take it from College table since I am displaying College details.
SELECT cc.committeeCollegeId as committeeCollegeId,
c.collegeId as collegeId,
cc.committeeMemberId as committeeMemberId
FROM committee_college as cc
left outer join College as c
on cc.collegeId = c.collegeId
where cc.committeeMemberId=:committeeMemberId
order by cc.committeeCollegeId asc
Can anyone tell how to display colleges based on its assignment to particular committeeMember?
You were close, you need INNER JOIN instead of LEFT JOIN:
SELECT DISTINCT C.typeName --<<== put here all the columns that you want in output
FROM committee_colleges CC
INNER JOIN college C
ON C.collegeId = CC.collegeId
WHERE CC.committeeMemberId = 2 --<<== your input parameter
EDIT: added DISTINCT
Hope it helps.
You can use below sql statement for the same
DECLARE #committeeMemberId INT = 2 -- Id of Committee member
;WITH CTE_MemberCommittee AS
(
SELECT CollegeId
FROM committee_colleges
WHERE committeeMemberId = #committeeMemberId
)
SELECT collegeId, typeName
FROM college
WHERE collegeId IN (SELECT CollegeId FROM CTE_MemberCommittee)
You can use simple inner join for that,
If you want collegename based on memberId use following query,
select a.collegeid,a.typeName from
college a, committee_colleges b, committe_member c
where a.collegeid = b.collegeid and
b.committeememberid = c.committeeMemberId
and c.committeeMemberId = '2'
If you want collegename based on committemember name then use following query,
select a.collegeid,a.typeName from
college a, committee_colleges b, committe_member c
where a.collegeid = b.collegeid and
b.committeememberid = c.committeeMemberId
and c.Name = 'xyz'
Hope it will help.
try this:
DECLARE #LoginCommitteeMemberId INT=2
SELECT t2.Name AS MemberName,
t3.TypeName AS CollageName
FROM committee_college t1
INNER JOIN Committee_Member t2
ON t1.committeeMemberId = t2.committeeMemberId
INNER JOIN College as t3
ON t1.collegeId = t3.collegeId
WHERE t1.committeeMemberId = #LoginCommitteeMemberId
I have a table with 3 columns: Code, Year, percentage.
I need to return the code with the lowest (minimal) percentage in 2009. After this, I want also the name of the code, that exsist in other table that I made.
I only think using CREATE VIEW, but I prefer not to do so.
Select table.code, table.year, table.percentage, othertable.name
from table
inner join othertable on table.FKId = othertable.PKid
where year = 2009
and percentage =
(select min(percentage)
from table
where year = 2009)
Updated to include the othertable... since we don't have names.
UPDATED
Now that we have table names... Updated 3rd time now that I know year is string.
Select E.Code, C.Name
From dbo.Exam E
inner join dbo.Course C
ON E.Code = C.Code
Where E.Year = '2009' and --<-- PROBLEM LIKELY HERE year was string not int.
E.Fail = (select MIN(E2.Fail)
from dbo.Exam E2 where E2.Year = '2009') --<--Don't forget here too.
From comments: sample Data:
INSERT INTO Exam VALUES(333,'2009',40)
INSERT INTO Exam VALUES(333,'2009',20)
INSERT INTO Exam VALUES(555,'2009',19)
INSERT INTO Exam VALUES(444,'2009',19)
INSERT INTO Exam VALUES(777,'2009',23)
INSERT INTO Exam VALUES(333,'2009',0)
INSERT INTO Course VALUES(111,'Name1',5)
INSERT INTO Course VALUES(333,'Name2',5)
INSERT INTO Course VALUES(444,'Name3',6)
INSERT INTO Course VALUES(555,'Name4',3)
INSERT INTO Course VALUES(777,'Name5',3)
INSERT INTO Course VALUES(999,'Name6',6)
Assumption is result should be
Name2, 5
You can use a group by to find the lowest percentage for a year, and then join back to the main tables to find the corresponding other columns:
select *
from CodeYearPercTbl cyp
join CodeTbl c
on c.Code = cyp.Code
join (
select Year
, min(Percentage) as MinPerc
from CodeYearPercTbl
group by
Year
) as filter
on filter.Year = cyp.Year
and filter.MinPerc = cyp.Percentage
where cyp.Year = 2009
Table-1 : Code,Year,Percentage
Table-2 : Code,CodeName
select T1.Code,T2.CodeName,T1.Percentage from
(
select TOP 1 Code,Percentage
from Table-1
where Year = '2009'
order by Percentage asc
) T1 inner join Table-2 T2 on T1.Code = T2.Code
Try this:
select a.Code, c.Name
from YourTable a inner join AnotherTable c on a.Code = c.Code
where a.Percentage = (select MIN(Percentage)
from YourTable b where b.Year = '2009'
)
I'm trying to make a query that looks at a single table to see if a student is in a team called CMHT and in a medic team - if they are I don't want to see the result.
I only want see the record if they're only in CMHT or medic, not both.
Would the right direction be using sub query to filter it out? I've done a search on NOT IN but how could you get to see check if its in more then 2 teams are not?
Student Team ref
1 CMHT 1
1 Medic 2
2 Medic 3 this would be in the result
3 CMHT 5 this would be in the result
So far I've done the following code would I need use a sub query or do a self join and filter it that way?
SELECT Table1.Student, Table1.Team, Table1.refnumber
FROM Table1
WHERE (((Table1.Team) In ('Medics','CMHT'))
This is Mark Byers's answer with a HAVING clause instead of a subquery:
SELECT Student, Team, ref
FROM Table1
GROUP BY Student
HAVING COUNT(Student) = 1
SELECT *
FROM students
WHERE NOT EXISTS
(
SELECT NULL
FROM students si
WHERE si.student = s.student
AND si.team = 'CMHT'
)
OR NOT EXISTS
(
SELECT NULL
FROM students si
WHERE si.student = s.student
AND si.team = 'Medic'
)
SELECT a.*
FROM Table1 a
INNER JOIN
( SELECT Student, COUNT(*) FROM Table1
GROUP BY Student
HAVING COUNT(*) = 1)b
ON (a.Student = b.Student)
how could you get to see check if its in 2 or more teams?
You can count the number of teams per student and then filter only those you want to see:
SELECT student FROM
(
SELECT student, COUNT(*) AS cnt
FROM Table1
GROUP BY student
) T1
WHERE cnt = 1
You can do it with outer join
select COALESCE(t1.Student, t2.Student) as Student,
COALESCE(t1.Team, t2.Team) as Team,
COALESCE(t1.ref, t2.ref) as ref
from
(select * from Student where Team = 'CMHT') t1
outer join
(select * from Student where Team = 'Medic') t2
on t1.Student = t2.Student
where
t1.Student is null or
t2.Student is null;