We have the following schema:
instructor(ID, name, dept name, salary)
teaches(ID, course id, sec id, semester, year)
Find instructors who taught the most courses in 2009. Can someone please help me? I'm confused how to write this out in relational algebra.
This must be homework ;-) So I'll give you some hints...
Since I haven't done tuple relational calculus since college (http://en.wikipedia.org/wiki/Relational_algebra), here is an approximation in sql,
select instructor.ID, instructor.name, count(teaches.ID)
from instructor
join teaches on teaches.ID = instructor.ID
and count(teaches.ID) >= ...
group by ...
Leaving you to fill in the group by and >= values.
Think about how you calculate how many courses each teacher teaches,
select teaches.ID, count(*)
from teaches
group by teaches.ID
This might help: MySQL count maximum number of rows
Related
It's an exercise that is not solved in the book in which I am studying.
The goal is to find the seller who has had the highest number of sales per month,
during all the months for which there is registered information. The problem is that I do not know how to divide tuples into periods of one month.
First table is:
Table Sellers
Id_seller
Name_Product
And the other one is:
Table Product
Name_Product
View_datetime
Budget
What did i do?
I made this query:
SELECT id_seller FROM(SELECT id_seller, COUNT(id_seller)
FROM SELLERS INNER JOIN PRODUCT
ON SELLERS.name_product = PRODUCT.name_product
GROUP BY id_seller HAVING COUNT(id_seller)>= 1
ORDER BY 2 DESC)
WHERE ROWNUM = 1;
The query returns me the seller that most sales has done, but not "per month since there are records" as the statement asks. Any ideas? I'm so lost...
The idea is to compare the total sales of each salesman in this month (sysdate), with those of a month ago, two months ago ... so long as there are older records. And get the maximum from each seller. And then you print the seller with more sales from the previous list. If a seller sells 400 products this month(April, the sysdate), but another seller sold in October last year 500, the result would be the second seller . That's what I do not know how to do.
Thanks ^^
You could try this query
select MonthName, id_seller, max(TotalSales) from (
select to_char(sysdate, 'Month') MonthName, sellers.id_seller, count(sellers.id_seller) TotalSales
from sellers inner join product
on sellers.name_product = product.name_product
group by to_char(view_datetime, 'Month'), sellers.id_seller
) tab
group by MonthName, id_seller
There are a few points to make...
The tables are weird. I assume your table sellers would better be called sales, right?
In this example, having count... >= 1 is a no-op. Count could only be 0 if there were no rows at all, in which case there would be no row in the group- by output. You can just leave this count away, here.
To get the sales per month, just add the month to the group by. I.e. group by id_seller, To_date(view_datetime,'YYYYMM').
I have a table called loan with loan amount,annual income, year (MMM-YY format) and member id. I am trying to find the highest loan amount in a year along wit annual income and member id details.
I tried to group the highest loan amount by year using the code
select max(cast(loan_amt as int)),issue_d from loan group by issue_d;
then I wanted also to fetch the member id and annual income information so I wrote the following code
but it is giving me error message for using alias for a column which is cast.
Code:
select a.loan_amt,a.member_id,a.annual_inc,a.issue_d
from
(select loan_amt,member_id,annual_inc,issue_d from loan) a
join
(select max(cast(loan_amt as int)) as ml,issue_d from loan group by issue_d) c
where ((a.issue_d=c.issue_d) and (a.loan_amt=a.ml));
What you want to do is rank the records based on the Amount, per Period, then keep only the top 1 record for each Period.
Use one of the analytic functions that are designed exactly for that purpose -- Hive has a pretty good support of the SQL standard on that topic.
Since you don't say what to do about ties (i.e. what if several loans have the same Amount???) I assume you want just one record chosen randomly...
select X, Y, Z, Period, Amount as TopAmount
from
(select X, Y, Z, Period, cast(StrAmt as double) as Amount,
row_number() over (partition by Period order by cast(StrAmt as double) desc) as TmpRank
from WTF
) TMPWTF
where TmpRank =1
If you want all the records with top Amount then replace row_number with rank or dense_rank (the "dense" stuff would make a difference for the top 2, but not for the top 1)
Using Oracle, PSQL, I am trying to figure out the earliest invoice date for each supplier. That would be simple enough, but I am also trying to figure out the max distribution line on the earliest invoice so I can determine what segment of the business the invoice belongs to. Segment is determined by SEGMENT_NUMBER in the example below. I know a sub query or multiple sub queries are needed here with a group by clause but I am at a loss. The syntax below is not even close, but I wanted to provided something for feedback.
SELECT
SUPPLIER_ID,
INVOICE_NUMBER,
SEGMENT_NUMBER,
MIN(INVOICE_DATE) as EARLIEST_INV_DATE,
MAX(DISTRIBUTION_AMOUNT) as MAX_DIST_LINE
FROM INVOICE_DIST
Use Analytical function like RANK().
SELECT SUPPLIER_ID,
INVOICE_NUMBER,
SEGMENT_NUMBER,
INVOICE_DATE,DISTRIBUTION_AMOUNT
(SELECT SUPPLIER_ID,
INVOICE_NUMBER,
SEGMENT_NUMBER,
INVOICE_DATE,DISTRIBUTION_AMOUNT,
RANK() OVER(PARTITION BY SUPPLIER_ID ORDER BY INVOICE_DATE,DISTRIBUTION_AMOUNT DESC) POSITION FROM INVOICE_DIST) TBL WHERE POSITION=1;
table a and table b, table a has two field, field 1 and 2, and table b has two fields, field 3 and 4.
where
tablea.field1 >= 4 and tableb.field3 = 'male'
is something like the above query possible, Ive tried something like this in my database although there are not errors and i get results, it checks whether both are true separately.
im going to try to be abit clear, and cant give out the query outright as much as i would like to (University reasons). so ill explain, table 1 has several columns of information one of which is number of kids, table two has more information on said kids, like gender.
so im having trouble creating a query where first it checks that a parent has 2 kids but two male kids, thus creating a relationship between parent table and kids table.
CREATE TABLE parent
(pID NUMBER,
numberkids INTEGER)
CREATE TABLE kids
(kID NUMBER,
father NUMBER,
mother NUMBER,
gender VARCHAR(7))
select
p.pid
from
kids k
inner join parent pm on pm.pid = k.mother
inner join parent pf on pf.pid = k.father,
parent p
where
p.numberkids >= 2 and k.gender = 'male'
/
this query checks that the parent has 2 kids or more and the kids gender is male, but i need it to check whether the parent has 2 kids and OF those kids is there 2 or more male kids (or in short to check whether the parent has 2 or more male kids).
sorry for the long winded explanation i modified the tables and the query from the one im actually going to use (so some mistakes might be there, but the original query work, just not how i want explained above). any help would be greatly appreciated.
The best thing to do would be to take the numberKids column out of the parent table ... you'll find it very difficult to maintain.
Anyway, something like this might do the trick:
SELECT p.pID
FROM parent p INNER JOIN kids k
ON p.pID IN (k.father, k.mother)
WHERE k.gender = 'male'
GROUP BY p.pID
HAVING COUNT(*) >= 2;
I have been asked this question;
You list county names and the surnames of the representatives if the representatives in the counties have the same surname.
and I have the following tables;
***REPRESENTATIVE***
REPI SURNAME FIRSTNAME COUNTY CONS
---- ---------- ---------- ---------- ----
R100 Gorege Larry kent CON1
R101 shneebly john kent CON2
R102 shneebly steve kent CON3
I cant seem to figure out the correct way to ask Orical to display a surname that exists more then twice and the surnames are in the same country.
I know how to ask WHERE something = something, but that's doesn't ask what I want to know.
It sounds like you want to use the HAVING clause after doing a GROUP BY
SELECT surname, county, count(*)
FROM you_table
GROUP BY surname, county
HAVING count(*) > 1;
If you really mean "more than twice" as you wrote, none of the data you'd want HAVING count(*) > 2 but then none of your sample data would be returned.
In words, this SQL statement says
Group the data into buckets by surname and county. Each distinct combination of surname and county is a separate bucket.
Count the number of rows in each bucket
Return those buckets where there are at least two rows