I’ve ran in to some problems with the following SQL assignment. I’m to retrieve the ID, firstname and lastname of any member who is registered in section that contains the word ‘xyz’.
So far I’ve managed the following:
SELECT m.id, p.firstname, p.lastname FROM member m
INNER JOIN person p ON m.id = p.id
WHERE m.id IN (SELECT id FROM membersection);
How do I go forward from here? I have no idea how to retrieve the sectionid from the membersection table then fetch the section name from the section id using that ID so I can check if the section name contains the previously stated word.
member:
id
member_number
registration_date
membersection:
memberid
sectionid
person:
id
firstname
lastname
section:
id
name
Just keep joining. And in the end use LIKE to check if section.name contains 'xyz'.
SELECT m.id,
p.firstname,
p.lastname
FROM member m
INNER JOIN person p
ON p.id = m.id
INNER JOIN membersection ms
ON ms.memberid = m.id
INNER JOIN section s
ON s.id = ms.sectionid
WHERE s.name LIKE '%xyz%';
There is some ambiguity in your question with regards to how your data are structured; what are the primary and foreign keys?
But, making some assumptions, you're almost there, you can chain multiple join statements together:
select
m.id,
p.firstname,
p.lastname
from
member m
inner join person p on
m.id = p.id
inner join membersection ms on
m.id = ms.memberid
inner join section s on
ms.sectionid = s.id
where
s.name like '%xyz%'
It's not super obvious what's going on with your Data Relationships, but this would be the basic route you might want to take (LEFT JOIN as I do not know the relationship):
SELECT m.id, p.firstname, p.lastname, ms.sectionid
FROM member m
INNER JOIN person p ON m.id = p.id
LEFT JOIN section s ON m.id = s.id
LEFT JOIN membersection ms ON m.id = ms.memberid
WHERE s.name = 'xyz'
Related
I have the next query:
SELECT c.name as clientName, p.id as projectId, p.name as projectName, p.rate, u.name as userName, sum(w.duration) as workedHours
FROM Project p, User u, Worklog w, Client c
WHERE w.user_id = u.id AND w.project_id = p.id AND p.client_id = c.id
GROUP BY p.id, u.id
that returns the projects, clients, hourly rate and worked hours.
How should be changed to return also the projects where workedHours is equal with 0?
Because this query returns just the records where workedHours is not 0.
Thank you for your time.
The problem is that no row in worklog can be joined, and that your condition in the WHERE clause removes any row without worklog associated.
Solution 1 : Using a LEFT JOIN
Using a left join instead would solve your problem.
SELECT c.name as clientName, p.id as projectId, p.name as projectName, p.rate, u.name as userName, coalesce(sum(w.duration), 0) as workedHours
FROM Project p, User u, Client c
LEFT JOIN Worklog w ON w.project_id = p.id AND w.user_id = u.id
WHERE p.client_id = c.id
GROUP BY p.id, u.id
By the way your query is suspicious in other aspects. For example c.name is in the SELECT clause but not in the GROUP BY clause. I take it that you use MySQL which is the only RDBMS I'm aware of which allows such queries. You maybe should consider adding the retrieved columns in the GROUP BY clause.
Solution 2 : Using only ANSI JOINs
As underscore_d points out, you may want to avoid old-style joins completely, and preferable use the following query :
SELECT
c.name as clientName,
p.id as projectId,
p.name as projectName,
p.rate,
u.name as userName,
coalesce(sum(w.duration), 0) as workedHours
FROM Project p
CROSS JOIN User u
INNER JOIN Client c ON p.client_id = c.id
LEFT JOIN Worklog w ON w.project_id = p.id AND w.user_id = u.id
GROUP BY c.name, p.id, p.name, p.rate, u.id, u.name
Solution 3 - Using a subquery
Another solution is to use a subquery, which would allow you to remove the GROUP BY clause completely and get a more manageable query if you ever need to retrieve more information. I personally don't like long lists of columns in a GROUP BY clause.
SELECT
c.name as clientName,
p.id as projectId,
p.name as projectName,
p.rate,
u.name as userName,
(SELECT SUM(duration) FROM Worklog WHERE project_id = c.id AND user_id = u.id) as workedHours
FROM Project p
CROSS JOIN User u
INNER JOIN Client c ON p.client_id = p.id
You should use standard ANSI joins and use LEFT JOIN on worklog table and ultimately you have to use LEFT JOIN on the user table as follows:
SELECT C.NAME AS CLIENTNAME,
P.ID AS PROJECTID,
P.NAME AS PROJECTNAME,
P.RATE,
U.NAME AS USERNAME,
SUM(W.DURATION) AS WORKEDHOURS
FROM PROJECT P
JOIN CLIENT C
ON P.CLIENT_ID = C.ID
LEFT JOIN WORKLOG W
ON W.PROJECT_ID = P.ID
LEFT JOIN USER U
ON W.USER_ID = U.ID
GROUP BY P.ID,
U.ID;
I'm trying to create a Stored Procedure for my school project which uses Model First.
I wanted to make a SP for returning av list of games with most orders, as a 'top list' so to speak, but can't figure it out after searching for similiar threads. The parameter #antal should return the range of distinct results to give back. So let's say I send in 5 it should return 5 Products, and 3 should return 3 products and so forth...
Since I am new to this, I'm stuck. The code so far is:
use SpelAffarenDatabas
go
create procedure [dbo].[GetTopListGames]
(
#antal int
)
as
select distinct top (6) p.Id, p.Name, p.Orders, k.Name, g.Name from ProduktSet as p
left join ConsoleProduct as kp
on p.Id = kp.Product_Id
left join ConsoleSet as k
on kp.Console_Id = k.Id
left join ProductGenre as pg
on p.Id = pg.Product_Id
left join GenreSet as g
on pg.Genre_Id = g.Id
group by p.Id, p.Name, p.Orders, k.Name, g.Name
So how do I go about getting a proper response that gives me a proper response, whic I guess would be of distinct entities?
select distinct top (#antal) p.Id, p.Name, p.Orders, k.Name, g.Name from ProduktSet as p
left join ConsoleProduct as kp
on p.Id = kp.Product_Id
left join ConsoleSet as k
on kp.Console_Id = k.Id
left join ProductGenre as pg
on p.Id = pg.Product_Id
left join GenreSet as g
on pg.Genre_Id = g.Id
group by p.Id, p.Name, p.Orders, k.Name, g.Name
order by p.Orders Desc
I do realise that problem I am facing is not a rocket science but still, I did not find any information about fixing this.
I have multiple tables in my database (PSQL) I want to create a select query to make a reporting function for my app.
Here is my query:
select
s.id, s.name, st.name, p.firstname || ' ' || p.lastname,
f.name, f.store_date, bdt.name, bd.comment
from
system s, systemstatus st, role w, person p, file f,
documenttype bdt, document bd
where
w.system_id = s.id and
p.id = w.person_id and
st.id = s.status_id and
bd.system_id = s.id and
bd.file_id = f.id and
bd.type_id = bdt.id and
bd.role_id = w.id;
Query works I get 300 rows fully filled with values I am searching for. Problem is that I have about 1000 rows in System Table. It is possible that there is no Person or Document which could be linked with particular System.
I would like to see all rows that are in my System table (I mean about 1000), and when I can't link Person or Document with System I want the field to be null ( now it is not shown at all)
Main part of the answer is - you need left outer join.
Additional parts of the answer - use ANSI join syntax and format your queries:
select
s.id, s.name, st.name, p.firstname || ' ' || p.lastname, f.name,
f.store_date, bdt.name, bd.comment
from system as s
left outer join systemstatus as st on st.id= s.status_id
left outer join role as w on w.system_id = s.id
left outer join person as p on p.id = w.person_id
left outer join document as bd on bd.system_id = s.id and bd.role_id = w.id
left outer join documenttype as bdt on bdt.id = bd.type_id
left outer join file as f on f.id = bd.file_id
Always remember that somebody will read your code someday (may be it will be future you :) ) - so readability counts!
You are connecting your tables in query via "where" clause, which is equal to inner join. Instead you should left join Person and Document tables to System table, e.g.:
select *
from system s
left join role w on w.system_id = s.id
left join person p on p.id = w.person_id
So I want to count a number of books, but the books are stored in 2 different tables with the same attribute name.
I want to get a result that looks like:
name1 [total number of books of 1]
name2 [total number of books of 2]
I tried this triple join;
SELECT DISTINCT name, count(book)
FROM writes w
LEFT JOIN person p on p.id = w.author
LEFT JOIN book b on b.title = w.book
LEFT JOIN controls l on l.controller=p.id
GROUP BY name
ORDER BY name DESC
but since book exists as an attribute in writes and in controls, it cant execute the query.
It can only do it if I leave out one of joins so it can identify book.
How can I tell the sql engine to count the number of both book attributes together for each person?
As a result of database design that you interested in, you should issue 2 different sql and then merge them to handle single output.
A)
SELECT DISTINCT w.name as 'Name', count(w.book) as 'Cnt'
FROM writes w
LEFT JOIN person p on p.id = w.author
LEFT JOIN book b on b.title = w.book
B)
SELECT DISTINCT l.name as 'Name', count(l.book) as 'Cnt'
FROM controls l
LEFT JOIN person p on p.id = l.controller
LEFT JOIN book b on b.title = l.book
For your purpose, you can get UNION of A and B.
or you can use them as data source on a third SQL
select A.Name, sum(A.Cnt+B.Cnt)
from A, B
where A.Name = B.Name
group by A.Name
order by A.Name
WITH T AS
(
SELECT DISTINCT 'WRITES' FROMTABLE, w.name, w.count(book)
FROM writes w
LEFT JOIN person p on p.id = w.author
LEFT JOIN book b on b.title = w.book
GROUP BY name
UNION ALL
SELECT DISTINCT 'CONTROLLS' FROMTABLE, c.name, count(c.book)
FROM controlls c
LEFT JOIN person p on p.id = c.author
LEFT JOIN book b on b.title = c.book
GROUP BY name
)
SELECT * FROM T ORDER BY NAME
Should work.
HTH
This will work on a per distinct author's ID to how many books they've written. The pre-aggregation will return one record per author with how many books by that author. THEN, join to the person table to get the name. The reason I am leaving it by ID and Name of the author is... what if you have two authors "John Smith", but they have respective IDs of 123 and 389. You wouldn't want these rolled-up to the same person (or do you).
select
P.ID,
P.Name,
PreAgg.BooksPerAuthor
from
( select
w.author,
count(*) BooksPerAuthor
from
writes w
group by
w.author ) PreAgg
JOIN Person P
on PreAgg.Author = P.id
order by
P.Name
I need to select results from one table based on certain matching values in a couple of other tables. I have the following tables:
person: id, firstname, lastname
team: id, teamname
player: id, person_id(FK), team_id(FK)
coach: id, person_id(FK), team_id(FK)
I need to return all the coaches and players names for each team. I've only ever used inner joins, and it doesn't seem like I can use those here, so any idea how to do this?
This will give you the coach:
SELECT team.Teamname, person.Firstname, person.Lastname
FROM person
JOIN coach ON person.id = coach.person_id
JOIN team ON coach.team_id = team.id
And this will give you the players:
SELECT team.Teamname, person.Firstname, person.Lastname
FROM person
JOIN player ON person.id = player.person_id
JOIN team ON player.team_id = team.id
So, the non-elegant, simple answer is to just toss it all together with UNION.
Just use an OR in the join to Team
SELECT
P.firstname,
P.lastname,
T.teamname
FROM
person p id
LEFT JOIN player pl
ON p.id = pl.person_id
LEFT JOIN coach c
ON p.id = c.person_id
LEFT JOIN team t
ON pl.team_id = t.id
or.c.team_id = t.id
Or if you perfer if and your database has COALESCE
LEFT JOIN team t
ON COALESCE(pl.team_id,c.team_id) = t.id