I am trying to write a query to give a grade to a percentage
I have a table of percentages per student per paper (StuID, pct, paperID) and a table of grade boundaries (paperID, minScore, maxScore, Grade)
the idea being to have a query that gives me student name and the grade that falls between min and max scores for the pct.
ridiculoulsy easy (lookup) in a spreadsheet, and seems to be ridiculously hard in SQL. I am really trying to avoid exporting to Excel and calculating there, or hard coding the boundaries within a selection, but at the moment they seem to be my only options.
Any suggestions to keep this a)in SQL and b)as generalised as possible (ie I am going to want to reuse the query with different grade boundaries)
Due to (ridiculous) software constraints at work, I am limited to MS Access for my DB needs
thanks
Just be careful on how you handle the ranges. So check >= and < conditions and adjust to your case.
SELECT S.StuID, S.paperID, S.pct, G.Grade
FROM Student S
JOIN Grades G
ON S.grade >= G.minScore
AND S.grade < G.maxScore
Related
I have the following tables and their fields
They ask me for a query that seems to me quite complex, I have been going around for two days and trying things, it says:
It is desired to obtain the average age of female athletes, medal winners (gold, silver or bronze), for the different modalities of 'Artistic Gymnastics'. Analyze the possible contents of the result field in order to return only the expected values, even when there is no data of any specific value for the set of records displayed by the query. Specifically, we want to show the gender indicator of the athletes, the medal obtained, and the average age of these athletes. The age will be calculated by subtracting from the system date (SYSDATE), the date of birth of the athlete, dividing said value by 365. In order to avoid showing decimals, truncate (TRUNC) the result of the calculation of age. Order the results by the average age of the athletes.
Well right now I have this:
select person.gender,score.score
from person,athlete,score,competition,sport
where person.idperson = athlete.idathlete and
athlete.idathlete= score.idathlete and
competition.idsport = sport.idsport and
person.gender='F' and competition.idsport=18 and score.score in
('Gold','Silver','Bronze')
group by
person.gender,
score.score;
And I got this out
By adding the person.birthdate field instead of leaving 18 records of the 18 people who have a medal, I'm going to many more records.
Apart from that, I still have to draw the average age with SYSDATE and TRUNC that I try in many ways but I do not get it.
I see it very complicated or I'm a bit saturated from so much spinning, I need some help.
Reading the task you got, it seems that you're quite close to the solution. Have a look at the following query and its explanation, note the differences from your query, see if it helps.
select p.gender,
((sysdate - p.birthday) / 365) age,
s.score
from person p join athlete a on a.idathlete = p.idperson
left join score s on s.idathlete = a.idathlete
left join competition c on c.idcompetition = s.idcompetition
where p.gender = 'F'
and s.score in ('Gold', 'Silver', 'Bronze')
and c.idsport = 18
order by age;
when two dates are subtracted, the result is number of days. Dividing it by 365, you - roughly - get number of years (as each year has 365 days - that's for simplicity, of course, as not all years have that many days (hint: leap years)). The result is usually a decimal number, e.g. 23.912874918724. In order to avoid that, you were told to remove decimals, so - use TRUNC and get 23 as the result
although data model contains 5 tables, you don't have to use all of them in a query. Maybe the best approach is to go step-by-step. The first one would be to simply select all female athletes and calculate their age:
select p.gender,
((sysdate - p.birthday) / 365 age
from person p
where p.gender = 'F'
Note that I've used a table alias - I'd suggest you to use them too, as they make queries easier to read (table names can have really long names which don't help in readability). Also, always use table aliases to avoid confusion (which column belongs to which table)
Once you're satisfied with that result, move on to another table - athlete It is here just as a joining mechanism with the score table that contains ... well, scores. Note that I've used outer join for the score table because not all athletes have won the medal. I presume that this is what the task you've been given says:
... even when there is no data of any specific value for the set of records displayed by the query.
It is suggested that we - as developers - use explicit table joins which let you to see all joins separated from filters (which should be part of the WHERE clause). So:
NO : from person p, athlete a
where a.idathlete = p.idperson
and p.gender = 'F'
YES: from person p join athlete a on a.idathlete = p.idperson
where p.gender = 'F'
Then move to yet another table, and so forth.
Test frequently, all the time - don't skip steps. Move on to another one only when you're sure that the previous step's result is correct, as - in most cases - it won't automagically fix itself.
Suppose we have this relational schema
homebuilder(hID, hName, hStreet, hCity, hZip, hPhone)
model(hID, mID, mName, sqft, story) subdivision(sName,
sCity, sZip) offered(sName, hID, mID, price) lot(sName,
lotNum, lStAddr, lSize, lPremium) sold(sName, lotNum, hID, mID,
status)
I have problem by doing relational algebra for each subdivision , find the number of models offered and the average, minimum and maximum price of the models offered at that subdivision. Also display the result in descending order on the average price of a home.
I am done with SQL formula, but it hard for me to translate this SQL to relational algebra. Can someone help me?
Here is what I got so far:
SQL:=
SELECT S, avg (O.price), min (O.price), max (O.price), count(*)
FROM offered O, subdivision S
WHERE O.sName = S.sName
GROUP BY S.sName
ORDER BY 4 desc;
+1 to DPenner's comment: quite true that you can't do ordering in RA. (Although those q's and a's referenced seem to have some 'difficulties'.)
Another thing you can't do in RA (contra the SQL that JaveLeave shows) is to have anonymous columns referenced by position. If SQL were a sensible language (or indeed any sort of language at all), you could name the column in the SELECT clause ..., max (O.price) AS maxPrice, ... then ORDER BY maxPrice desc. But no, you can't do that. In SQL you have to repeat ORDER BY max (O.price) desc. (By the way, the question asked for ordering by average price, not max(?) That's column 2.)
Contrast that the RA Group operation returns a relation. And being a relation it must have attributes only addressable by name.
Back to the question as asked. The nearest you can get to an ordering is to put a column on each row with the ordinal position of this row relative to the overall table. Since the question asks for descending sequence, the first step is to find the subdivision with minimum average price and tag it with ordinal 1. Then select all but that one, get the minmium of those, tag it with 2. And in general: take all not tagged so far; get the minmum; tag it with highest tag so far +1; recurse. So you need the transitive closure operation (which is another 'missing' feature of standard RA). You can find some SQL code to achieve this sort of thing in comp.database.theory -- from memory Joe Celko gives examples.
Off-topic: I'm puzzled why courses/professors/textbooks in SQL also ask you to do impossible things in RA. Certainly it's good to have a grounding in RA. It's a powerful mental model to understand data structures that SQL only obscures. RA (as an algebra) underpins most SQL engines. But then why leave the impression that RA is some sort of 'poor cousin' to SQL? There are no commercial implementations of RA; there are no job advertisements for RA programmers. Why try to make it what it isn't?
The question is whether the query described below can be done without recourse to procedural logic, that is, can it be handled by SQL and a CTE and a windowing function alone? I'm using SQL Server 2012 but the question is not limited to that engine.
Suppose we have a national database of music teachers with 250,000 rows:
teacherName, address, city, state, zipcode, geolocation, primaryInstrument
where the geolocation column is a geography::point datatype with optimally tesselated index.
User wants the five closest guitar teachers to his location. A query using a windowing function performs well enough if we pick some arbitrary distance cutoff, say 50 miles, so that we are not selecting all 250,000 rows and then ranking them by distance and taking the closest 5.
But that arbitrary 50-mile radius cutoff might not always succeed in encompassing 5 teachers, if, for example, the user picks an instrument from a different culture, such as sitar or oud or balalaika; there might not be five teachers of such instruments within 50 miles of her location.
Also, now imagine we have a query where a conservatory of music has sent us a list of 250 singers, who are students who have been accepted to the school for the upcoming year, and they want us to send them the five closest voice coaches for each person on the list, so that those students can arrange to get some coaching before they arrive on campus. We have to scan the teachers database 250 times (i.e. scan the geolocation index) because those students all live at different places around the country.
So, I was wondering, is it possible, for that latter query involving a list of 250 student locations, to write a recursive query where the radius begins small, at 10 miles, say, and then increases by 10 miles with each iteration, until either a maximum radius of 100 miles has been reached or the required five (5) teachers have been found? And can it be done only for those students who have yet to be matched with the required 5 teachers?
I'm thinking it cannot be done with SQL alone, and must be done with looping and a temporary table--but maybe that's because I haven't figured out how to do it with SQL alone.
P.S. The primaryInstrument column could reduce the size of the set ranked by distance too but for the sake of this question forget about that.
EDIT: Here's an example query. The SINGER (submitted) dataset contains a column with the arbitrary radius to limit the geo-results to a smaller subset, but as stated above, that radius may define a circle (whose centerpoint is the student's geolocation) which might not encompass the required number of teachers. Sometimes the supplied datasets contain thousands of addresses, not merely a few hundred.
select TEACHERSRANKEDBYDISTANCE.* from
(
select STUDENTSANDTEACHERSINRADIUS.*,
rowpos = row_number()
over(partition by
STUDENTSANDTEACHERSINRADIUS.zipcode+STUDENTSANDTEACHERSINRADIUS.streetaddress
order by DistanceInMiles)
from
(
select
SINGER.name,
SINGER.streetaddress,
SINGER.city,
SINGER.state,
SINGER.zipcode,
TEACHERS.name as TEACHERname,
TEACHERS.streetaddress as TEACHERaddress,
TEACHERS.city as TEACHERcity,
TEACHERS.state as TEACHERstate,
TEACHERS.zipcode as TEACHERzip,
TEACHERS.teacherid,
geography::Point(SINGER.lat, SINGER.lon, 4326).STDistance(TEACHERS.geolocation)
/ (1.6 * 1000) as DistanceInMiles
from
SINGER left join TEACHERS
on
( TEACHERS.geolocation).STDistance( geography::Point(SINGER.lat, SINGER.lon, 4326))
< (SINGER.radius * (1.6 * 1000 ))
and TEACHERS.primaryInstrument='voice'
) as STUDENTSANDTEACHERSINRADIUS
) as TEACHERSRANKEDBYDISTANCE
where rowpos < 6 -- closest 5 is an abitrary requirement given to us
I think may be if you need just to get closest 5 teachers regardless of radius, you could write something like this. The Student will duplicate 5 time in this query, I don't know what do you want to get.
select
S.name,
S.streetaddress,
S.city,
S.state,
S.zipcode,
T.name as TEACHERname,
T.streetaddress as TEACHERaddress,
T.city as TEACHERcity,
T.state as TEACHERstate,
T.zipcode as TEACHERzip,
T.teacherid,
T.geolocation.STDistance(geography::Point(S.lat, S.lon, 4326))
/ (1.6 * 1000) as DistanceInMiles
from SINGER as S
outer apply (
select top 5 TT.*
from TEACHERS as TT
where TT.primaryInstrument='voice'
order by TT.geolocation.STDistance(geography::Point(S.lat, S.lon, 4326)) asc
) as T
I've been learning SQL for about a day now and I've run into a road bump. Please help me with the following questions:
STUDENT (**StudentNumber**, StudentName, TutorialNumber)
TUTORIAL (**TutorialNumber**, Day, Time, Room, TutorInCharge)
ASSESSMENT (**AssessmentNumber**, AssessmentTitle, MarkOutOf)
MARK (**AssessmentNumber**, **StudentNumber**, RawMark)
PK and FK are identified within "**". I need to generate queries that:
1) List of assessment tasks results showing: Assessment Number, Assessment Title, and average Raw Mark. I know how to use the avg function for a single column, but to display something for multiple columns... a little unsure here.
My attempt:
SELECT RawMark, AssessmentNumber, AsessmentTitle
FROM MARK, ASSESSMENT
WHERE RawMark = (SELECT (RawMark) FROM MARK)
AND MARK.AssessmentNumber = ASSESSMENT.AssessmentNumber;
2) Report on tutorial enrollment showing: Tutorial Number, Day, Room, Tutor in Charge and number of students enrolled. Same as the avg function, now for the count function. Would this require 2 queries?
3) List each student's Raw Mark in each of the assessment tasks showing: Assessment Number, Assessment Title, Student Number, Student Name, Raw Mark, Tutor in Charge and Time. Sort on Tutor in Charge, Day and Time.
Here is an example for the first one, just take the logic and see if you can expand it to the other questions. I find that these things can be hard to lear if you can't find any solid examples but once you get the hang of it you'll sort it out pretty quick.
1)
SELECT a.AssessmentNumber, a.AssessmentTitle, AVG(RawMark)
FROM ASSESSMENT a LEFT JOIN MARK m ON a.AssessmentNumber = m.AssessmentNumber
GROUP BY a.AssessmentNumber, a.AssessmentTitle
OR not using a left join or alias table names
SELECT ASSESSMENT.AssessmentNumber, ASSESSMENT.AssessmentTitle, AVG(RawMark)
FROM ASSESSMENT,MARK
WHERE ASSESSMENT.AssessmentNumber = MARK.AssessmentNumber
GROUP BY ASSESSMENT.AssessmentNumber, ASSESSMENT.AssessmentTitle
I've been stuck with the rather famous problem of ranking students by grade for a couple weeks now, and while I've learned much, I still haven't solved my problem (the ranks are generated, but the process is too slow):
I have a large table (320,000 rows) that contains the student codes (serves as an identifier, instead of their names), the students classroom, the test , the tests date, the subject, the question number and the students grade on that question. This table is the base for everything else that is calculated and its size makes all these calculations very very slow, to the point where I find me almost breaking everything here at work.
First, some intel on the school (very little info, required to understand the problem)
Here at the school we have weekly tests over several subjects. The school is also separated in classrooms with different purposes (one is focused on math, physics and chemistry, another one is focused on biology, and the last one focuses on history, Portuguese and geography). But they all do the same tests every week.
What we want to do is calculate the standard deviation for each question for everyone in the school (not per-classroom) and the average grade per question (also for everyone in the school), and then generate the following ranks (all of them per date):
-Rank per subject per classroom (with "raw" grades), Rank per subject considering the whole school (with "raw" grades) and Rank per subject considering the whole school (using normalized grades, with the standard deviation per question and the average grade per question information)
-The same ranks that were mentioned above, but not per Subject, considering instead all subjects
As you can see, after calculating the average grades and the standard deviations, we still need to calculate the sums of the grades on each question, and rank according to these sums (the actual subject/test grades). I've attacked this problem in a few ways:
1)
Created two tables, one with the grades per student per subject (fields: Students code, Students classroom, Date of test, Subject, Grade, Normalized Grade, Rank in Classroom, Rank in School, Rank in School using normalized grades) and another with the grades per student per test (all subjects taken into account, fields: Students code, Students classroom, Date of test, Grade, Normalized Grade, Rank in Classroom, Rank in School, Rank in School using normalized grades).
The insertion of data in these tables takes about 50 seconds
Then, I tried using SQL to rank, however, I ran into some problems:
-Access has no ROW_NUMBER or RANK functions, and thus I have to use queries with COUNT, like (below is just a simplified version):
SELECT 1+(SELECT Count(*) FROM grades_table_per_subject t2 WHERE
t2.Grade > t1.Grade AND t1.Date=t2.Date AND t1.Subject=t2.Subject) AS [Global Rank],
1+(SELECT Count(*) FROM grades_table_per_subject t3 WHERE t3.Grade > t1.Grade AND
t3.Date=t1.Date AND t3.Subject=t1.Subject AND t3.Classroom=t1.Classroom) AS
[Rank in classroom] FROM grades_table_per_subject;
There still is the rank with the normalized grades in the query above, but I omitted it.
The table grades_table_per_subject has about 45,000 lines and this query takes more than 15 minutes here, even with indexing (tried many different index combinations, even some odd ones when I saw that the ones that should work didn't).
I also tried to ORDER BY Count() DESC the inner selects, but I hit ctrl+break after 7 minutes and no results.
2)
Added the following fields to the tables above:
Rank in Classroom, Rank in School, Rank in School using normalized grades
Then I tried using VBA with DAO and manually update the Rank fields, running the following code (simplified version):
Set rs = CurrentDb.OpenRecordset("SELECT Classroom, Date, Subject, Grade, [Rank in classroom] FROM
grades_table_per_subject ORDER BY Date, Classroom, Subject, Grade DESC;", dbOpenDynaset)
...
...
rs.movefirst
i=1
While Not rs.eof
'Verifies if there was a change on either one of Subject, Classroom, Date and if so:
...
i = 1
...
rs.Edit
rs![Rank in classroom]=i
rs.Update
i = i + 1
rs.movenext
Wend
rs.close
This obviously builds only one of the ranks (in this case per subject per classroom), and it takes alone 3min 10sec.
I verified that it takes so long due to the writes on the table (rs.Edit and rs.Update are the culprits, commenting them makes the whole thing run in only 4 seconds), but I need the ranks written to the table to generate an access report later.
FINALLY:
I could generate all the ranks once and make ways for the users to access all the data very quickly, but the idea is that everything should be calculated on-the-fly. The times we have achieved, however, make this impossible.
Overall, the question to be asked is the following:
-Is there a way to calculate the ranks shown above through an Access Query under 10 seconds, or to use VBA and calculate-insert these ranks to the table in a similar time considering the size of the tables used here?
Also, I would love to see a list of efficient ranking algorithms, so that even if I can't do everything quickly, I can improve it as much as possible.
I could generate all the ranks once and make ways for the users to access all the data very quickly, but the idea is that everything should be calculated on-the-fly.
Why?
Why bother regenerating the same data over and over? It's most likely preferable to generate these statistics when the data changes and just look them up every other time. Redoing work you've already done whenever somebody wants to check something is just silly.
I just saw you say ms access only
so ignore this answer -- or consider moving to a real DB if you want to be able to do this type of power processing.
original answer below
I don't have access to your test data, but how fast does this run?
SELECT RANK () OVER (PARTITION BY [Date],[Subject] ORDER BY Grade) AS [Global Rank],
RANK () OVER (PARTITION BY [Date],[Subject], Classroom ORDER BY Grade) AS [Rank in classroom]
FROM grades_table_per_subject
My guess is you are not going to be able to beat SQL Servers ranking speed in VBA, if this is not fast enough then you need to look in the profiler and see what indexes it suggests you make.