using oracle live sql trying to display a "Standings" view,
two tables in use would be MATCH and TEAM
so every time MATCH.WIN_TEAM = the id of a team it shows as a count
I guess I'm having issues with my count function. I know i can easily pull up where
so it would be
TEAM_NAME WINS
This is pulling up just the teams,subquery isn't working. am i on the right track?
select A.TEAM, B.W
from TEAM A
left join
(
select MATCH.WIN_TEAM,
Count(MATCH.WIN_TEAM) as W
from MATCH
group by MATCH.WIN_TEAM
) B
on A.ID = B.WIN_TEAM
order by B.W desc;
im a newb, halp. I'm guessing i need aliases too?
select TEAM.NAME ,copy_match.count_match
from TEAM
left join (select MATCH.WIN_TEAM as WIN_TEAM,
Count(MATCH.WIN_TEAM) AS count_match
from MATCH
group by MATCH.WIN_TEAM
) copy_match
on TEAM.ID=copy_match.WIN_TEAM;
Even if, technically, it works, I think you are over complicating your query
select TEAM.NAME ,COUNT(MATCH.WIN_TEAM)
from TEAM
left join
MATCH ON TEAM.ID=MATCH.WIN_TEAM
GROUP BY TEAM.NAME
ORDER BY COUNT(MATCH.WIN_TEAM)
Isn't this version a little easier ? Or maybe i missed a detail
Related
We need to query the DB for students whose points are greater than the average for the uni they go to. Now, in the handbook, it is used with GROUP BY clause, but I fail to understand why one is needed here at all if the universities are already grouped in the inner query's WHERE condition. Could you someone please shed some light on this matter?
SELECT snum, stu_name, uni_name, points
FROM Students
INNER JOIN Applications a1 USING (snum)
WHERE points > (SELECT AVG(points)
FROM Students
INNER JOIN Applications a2 USING (snum)
WHERE a2.uni_name = a1.uni_name
GROUP BY uni_name);
The GROUP BY is not needed and I wouldn't recommend using it. Just use:
SELECT s.snum, s.stu_name, a.uni_name, points
FROM Students s INNER JOIN
Applications a USING (snum)
WHERE points > (SELECT AVG(points)
FROM Students s2 INNER JOIN
Applications a2
USING (snum)
WHERE a2.uni_name = a.uni_name
);
In this case, the two are equivalent. But if you make a mistake, then using GROUP BY can return multiple rows -- and your query results in an error.
I would also suggest that you qualify all column names and give all tables meaningful aliases.
I need to use INNER JOINs to get a series of information and then I need to COUNT this info. I need to be able to "View all courses and the instructor taking them, the capacity of the course, and the number of members currently booked on the course."
To get all the info I have done the following query:
SELECT
C.coursename, Instructors.fname, Instructors.lname,C.maxNo, membercourse.memno
FROM Courses AS C
INNER JOIN Instructors ON C.instructorNo = Instructors.instructorNo
INNER JOIN Membercourse ON C.courseID = Membercourse.courseID;
but no matter where I put the COUNT it always tells me that whatever is outside the COUNT should be in the GROUP BY
I have worked out how to COUNT/GROUP BY the necessary info e.g.:
SELECT courseID, COUNT (DISTINCT MC.memno)
FROM Membercourse AS MC
GROUP BY MC.courseID;
but I don't know how to combine the two!
I think what you're looking for is a subquery. I'm a SQL-Server guy (not postgresql) but the concept looks to be almost identical after some crash-course postgresql googling.
Anyway, basically, when you write a SELECT statement, you can use a subquery instead of an actual table. So your SQL would look something like:
select count(*)
from
(
select stuff from table
inner join someOtherTable
)
... hopefully that makes sense. Instead of trying to write one big query where you're doing both the inner join and count, you're writing two: an inner one that gets your inner-join'ed data, and then an outer one to actually count the rows.
EDIT: To help explain a bit more on the thought process behind subqueries.
Subqueries are a way of logically breaking down the steps/processes on the data. Instead of trying to do everything in one big step, you do it in steps.
In this case, what's step one? It's to get a combined data source for your combined, inner-join'ed data.
Step 1: Write the Inner Join query
SELECT
C.coursename, Instructors.fname, Instructors.lname,C.maxNo,
membercourse.memno
FROM Courses AS C
INNER JOIN Instructors ON C.instructorNo = Instructors.instructorNo
INNER JOIN Membercourse ON C.courseID = Membercourse.courseID;
Okay, now, what next?
Well, let's say we want to get a count of how many entries there are for each 'memno' in that result above.
Instead of trying to figure out how to modify that query above, we instead use it as a data source, like it was a table itself.
Step 2 - Make it A Subquery
select * from
(
SELECT
C.coursename, Instructors.fname, Instructors.lname,C.maxNo,
membercourse.memno
FROM Courses AS C
INNER JOIN Instructors ON C.instructorNo = Instructors.instructorNo
INNER JOIN Membercourse ON C.courseID = Membercourse.courseID
) mySubQuery
Step 3 - Modify your outer query to get the data you want.
Well, we wanted to group by 'memno', and get the count, right? So...
select memno, count(*)
from
(
-- all that same subquery stuff
) mySubQuery
group by memno
... make sense? Once you've got your subquery written out, you don't need to worry about it any more - you just treat it like a table you're working with.
This is actually incredibly important, and makes it much easier to read more intricate queries - especially since you can name your subqueries in a way that explains what the subquery represents data-wise.
There are many ways to solve this, such using Window Functions and so on. But you can also achieve it using a simple subquery:
SELECT
C.coursename,
Instructors.fname,
Instructors.lname,
C.maxNo,
(SELECT
COUNT(*)
FROM
membercourse
WHERE
C.courseID = Membercourse.courseID) AS members
FROM
Courses AS C
INNER JOIN Instructors ON C.instructorNo = Instructors.instructorNo;
I couldn't be more specific in the title part but I want to do something a little bit complex for me. I thought I did it but it turned out that it is buggy.
I have three tables as following:
ProjectTable
idProject
title
idOwner
OfferTable
idOffer
idProject
idAccount
AccountTable
idAccount
Username
Now in one query I aim to list all the projects with most offers made, and in the query I also want to get details like the username of the owner, username of the offerer* etc. So I don't have to query again for each project.
Here is my broken query, it's my first experiment with GROUP BY and I probably didn't quite get it.
SELECT Project.addDate,Project.idOwner ,Account.Username,Project.idProject,
Project.Price,COUNT(Project.idProject) as offercount
FROM Project
INNER JOIN Offer
ON Project.idProject= Offer.idProject
INNER JOIN Account
ON Account.idAccount = Project.idOwner
GROUP BY Project.addDate,Project.idOwner,
Account.Username,Project.idProject,Project.Price
ORDER BY addDate DESC
*:I wrote that without thinking I was just trying to come up with example extra information, that is meaningless thanks to Hosam Aly.
Try this (modified for projects with no offers):
SELECT
Project.addDate,
Project.idOwner,
Account.Username,
Project.idProject,
Project.Price,
ISNULL(q.offercount, 0) AS offercount
FROM
(
SELECT
o.idProject,
COUNT(o.idProject) as offercount
FROM Offer o
GROUP BY o.idProject
) AS q
RIGHT JOIN Project ON Project.idProject = q.idProject
INNER JOIN Account ON Account.idAccount = Project.idOwner
ORDER BY addDate DESC
I might switch the query slightly to this:
select p.addDate,
p.idOwner,
a.Username,
p.idProject,
p.price,
o.OfferCount
from project p
left join
(
select count(*) OfferCount, idproject
from offer
group by idproject
) o
on p.idproject = o.idproject
left join account a
on p.idowner = a.idaccount
This way, you are getting the count by the projectid and not based on all of the other fields you are grouping by. I am also using a LEFT JOIN in the event the projectid or other id doesn't exist in the other tables, you will still return data.
Your question is a bit vague, but here are some pointers:
To list the projects "with most offers made", ORDER BY offercount.
You're essentially querying for projects, so you should GROUP BY Project.idProject first before the other fields.
You're querying for the number of offers made on each project, yet you ask about offer details. It doesn't really make sense (syntax-wise) to ask for the two pieces of information together. If you want to get the total number of offers, repeated in every record of the result, along with offer information, you'll have to use an inner query for that.
An inner query can be made either in the FROM clause, as suggested by other answers, or directly in the SELECT clause, like so:
SELECT Project.idProject,
(SELECT COUNT(Offer.idOffer)
FROM Offer
WHERE Offer.idProject = Project.idProject
) AS OfferCount
FROM Project
Is is possible to accomplish the equivalent of a LEFT JOIN with subselect where multiple columns are required.
Here's what I mean.
SELECT m.*, (SELECT * FROM model WHERE id = m.id LIMIT 1) AS models FROM make m
As it stands now doing this gives me a 'Operand should contain 1 column(s)' error.
Yes I know this is possible with LEFT JOIN, but I was told it was possible with subselect to I'm curious as to how it's done.
There are many practical uses for what you suggest.
This hypothetical query would return the most recent release_date (contrived example) for any make with at least one release_date, and null for any make with no release_date:
SELECT m.make_name,
sub.max_release_date
FROM make m
LEFT JOIN
(SELECT id,
max(release_date) as max_release_date
FROM make
GROUP BY 1) sub
ON sub.id = m.id
A subselect can only have one column returned from it, so you would need one subselect for each column that you would want returned from the model table.
I am attempting to get the information from one table (games) and count the entries in another table (tickets) that correspond to each entry in the first. I want each entry in the first table to be returned even if there aren't any entries in the second. My query is as follows:
SELECT g.*, count(*)
FROM games g, tickets t
WHERE (t.game_number = g.game_number
OR NOT EXISTS (SELECT * FROM tickets t2 WHERE t2.game_number=g.game_number))
GROUP BY t.game_number;
What am I doing wrong?
You need to do a left-join:
SELECT g.Game_Number, g.PutColumnsHere, count(t.Game_Number)
FROM games g
LEFT JOIN tickets t ON g.Game_Number = t.Game_Number
GROUP BY g.Game_Number, g.PutColumnsHere
Alternatively, I think this is a little clearer with a correlated subquery:
SELECT g.Game_Number, G.PutColumnsHere,
(SELECT COUNT(*) FROM Tickets T WHERE t.Game_Number = g.Game_Number) Tickets_Count
FROM Games g
Just make sure you check the query plan to confirm that the optimizer interprets this well.
You need to learn more about how to use joins in SQL:
SELECT g.*, count(*)
FROM games g
LEFT OUTER JOIN tickets t
USING (game_number)
GROUP BY g.game_number;
Note that unlike some database brands, MySQL permits you to list many columns in the select-list even if you only GROUP BY their primary key. As long as the columns in your select-list are functionally dependent on the GROUP BY column, the result is unambiguous.
Other brands of database (Microsoft, Firebird, etc.) give you an error if you list any columns in the select-list without including them in GROUP BY or in an aggregate function.
"FROM games g, tickets t" is the problem line. This performs an inner join. Any where clause can't add on to this. I think you want a LEFT OUTER JOIN.