I am working on a class question so please dont provide a direct answer but some guidance please.
I have joined 3 tables (businesses, categories, and countries). I need to now answer the following question: "Which are the most common categories for the oldest businesses on each
continent?"
Here is the code that works to join the tables:
SELECT bus.business,
bus.year_founded,
bus.category_code,
bus.country_code,
cat.category,
cou.continent
FROM businesses AS bus
INNER JOIN categories AS cat
ON bus.category_code = cat.category_code
INNER JOIN countries AS cou
ON bus.country_code = cou.country_code
ORDER BY year_founded
I have the 3 tables joined but now need to run an additional query to answer the above question. I have tried writing the COUNT or MIN functions with the initial SELECT for the joins however that throws an error. I also tried using GROUP BY function at the end of the join but also get an error.
Any suggestions would be appreciated
Related
I'm trying to do this query to display the names of the stores and the quantity of each book sold with only using joins but I tried to use
SELECT DISTINCT x.stor_name, t.title, s.qty
FROM stores x
INNER JOIN discounts d
ON x.stor_id=d.stor_id
INNER JOIN salesdetail s
ON d.stor_id=s.stor_id
INNER JOIN titles t
ON s.title_id=t.title_id
ORDER BY s.qty desc;
but that only displayed one of the stores results set for 'Bookbeat'.
I tried to use Left, Right & Full Outer joins to no avail so I'm wondering how I would go about doing that query to display the names for the other stores that are not displaying their result set. As there is 7 stores and only 1 is displaying it's results.
The link is a pastebin to the database.
And this is the schema.
It's hard to say without more information about your schema - it strikes me as wrong-ish that you're joining to discounts only on stor_id. I'd expect discounts to be applied to different titles, not store-wide... and I wouldn't expect discounts to be always-enabled. Try running it without the discounts inner join. Futzing around with "Distinct" and outer joins is almost always the wrong approach with things like this
I see from your profile you're a first-year. Is this schoolwork? How do I ask and answer homework questions?
I'm working on enhancing a query for a DB2 database and I'm having some problems getting acceptable performance due to the number of joins across large tables that need to be performed to get all of the data and I'm hoping that there's a SQL function or technique that can simplify and speed up the process.
To break it down, let's say there are two tables: People and Groups. Groups contain multiple people, and a person can be part of multiple groups. It's a many-to-many, but bear with me. Basically, there's a subquery that will return a set of groups. From that, I can join to People (which requires additional joins across other tables) to get all of the people from those groups. However, I also need to know all of the groups that those people are in, which means joining back to the Groups table again (several more joins) to get a superset of the original subquery. There are additional joins in the query as well to get other pieces of relevant data, and the cost is adding up in a very ugly way. I also need to return information from both tables, so that rules out a number of techniques.
What I'd like to do is be able to start with the People table, join it to Groups, and then compare Groups with the subquery. If the Groups attached to one person has one match in the subquery, it should return ALL Group items associated with that person.
Essentially, let's say that Bob is part of Group A, B, and C. Currently, I start with groups, and let's say that only Group A comes out of the subquery. Then I join A to Bob, but then I have to come back and join Bob to Group again to get B and C. SQL example:
SELECT p.*, g2.*
FROM GROUP g
JOIN LINKA link
ON link.GROUPID = g.GROUPID
JOIN LINKB link1
ON link1.LISTID = link.LISTID
JOIN PERSON p
ON link1.PERSONID = p.PERSONID
JOIN LINKB link2
ON link2.PERSONID = p.PERSONID
JOIN LINKA link3
ON link2.LISTID = link3.LISTID
JOIN GROUP g2
ON link3.GROUPID = g2.GROUPID
WHERE
g.GROUPID IN (subquery)
Yes, the linking tables aren't ideal, but they're basically normalized tables containing additional information that is not relevant to the query I'm running. We have to start with a filtered Group set, join to People, then come back to get all of the Groups that the People are associated to.
What I'd like to do is start with People, join to Group, and if ANY Group that Bob is in returns from the subquery, ALL should be returned, so if we have Bob joined to A, B, and C, and A is in the subquery, it will return three rows of Bob to A, B, and C as there was at least one match. In this way, it could be treated as a one-to-many relationship if we're only concerned with the Groups for each Person and not the other way around. SQL example:
SELECT p.*, g.*
FROM PEOPLE p
JOIN LINKB link
ON link.PERSONID = p.PERSONID
JOIN LINKA link1
ON link.LISTID = link1.LISTID
JOIN GROUP g
ON link1.GROUPID = g.GROUPID
WHERE
--SQL function, expression, or other method to return
--all groups for any person who is part of any group contained in the subquery
The number of joins in the first query make it largely unusable as these are some pretty big tables. The second would be far more ideal if this sort of thing is possible.
From the question, I think you are querying hierarchical data. DB2 provides facility to deal with such data. There are two clauses Start with and Connect by in DB2 which will be useful. They are explained here.
Consider the two tables' schema:
1) Person(name varchar(100),income int)
2) IncomeGroups(incomeGroupName varchar(100), minIncome int, maxIncome int)
I was stumbled while developing a sql query for fetching Person Names with their IncomeGroupNames based on their income.
I am trying to accomplish something like (Name,IncomeGroupName).
Is it even possible? I'll be really glad if anyone can guide me in this.
SELECT a.Name, b.IncomeGroupName
FROM Person a
INNER JOIN IncomeGroups b
ON a.income BETWEEN b.minIncome AND b.maxIncome
To further gain more knowledge about joins, kindly visit the link below:
Visual Representation of SQL Joins
You can use the following query which joins the tables:
select p.name,
i.incomeGroupName
from person p
inner join incomegroups i
on p.income >= i.minIncome
and p.income <= i.maxIncome;
See SQL Fiddle with Demo
This joins the tables based on the range that the person's income falls in.
I have two tables, Invoices and members, connected by PK/FK relationship through the field InvoiceNum. I have created the following sql and it works fine, and pulls 44 records as expected.
SELECT
INVOICES.InvoiceNum,
INVOICES.GroupNum,
INVOICES.DivisionNum,
INVOICES.DateBillFrom,
INVOICES.DateBillTo
FROM INVOICES
INNER JOIN MEMBERS ON INVOICES.InvoiceNum = MEMBERS.InvoiceNum
WHERE MEMBERS.MemberNum = '20032526000'
Now, I want to replace INVOICES.GroupNum and INVOICES.DivisionNum in the above query with GroupName and DivisionName. These values are present in the Groups and Divisions tables which also have the corresponding Group_num and Division_num fields. I have created the following sql. The problem is that it now pulls 528 records instead of 44!
SELECT
INVOICES.InvoiceNum,
INVOICES.DateBillFrom,
INVOICES.DateBillTo,
DIVISIONS.DIVISION_NAME,
GROUPS.GROUP_NAME
FROM INVOICES
INNER JOIN MEMBERS ON INVOICES.InvoiceNum = MEMBERS.InvoiceNum
INNER JOIN GROUPS ON INVOICES.GroupNum = GROUPS.Group_Num
INNER JOIN DIVISIONS ON INVOICES.DivisionNum = DIVISIONS.Division_Num
WHERE MEMBERS.MemberNum = '20032526000'
Any help is greatly appreciated.
You have at least one relation between your tables which is missing in your query. It gives you extra records. Find all common fields. Say, are divisions related to groups?
The statement is fine, as far as the SQL syntax goes.
But the question you have to ask yourself (and answer it):
How many rows in Groups do you get for that given GroupNum?
Ditto for Divisions - how many rows exist for that DivisionNum?
It would appear that those numbers aren't unique - multiple rows exist for each number - therefore you get multiple rows returned
I have a table B with cids and cities. I also have a table C that has these cids with extra information. I want to list all the cids in table C that are associated with ALL appearances of a given city in Table B.
My current solution relies on counting the number of times the given city appears in Table B and selecting only the cids that appear that many times. I don't know all the SQL syntax yet, but is there a way to select for this kind of pattern?
My current solution:
SELECT Agents.aid
FROM Agents, Customers, Orders
WHERE (Customers.city='Duluth')
AND (Agents.aid = Orders.aid)
AND (Customers.cid = Orders.cid)
GROUP BY Agents.aid
HAVING count(Agents.aid) > 1
It only works because I know right now with the HAVING statement.
Thanks for the help. I wasn't sure how to google this problem, since it's pretty specific.
EDIT: I'm pinpointing my problem a bit. I need to know how to determine if EVERY row in a table has a certain value for a field. Declaring a variable and counting the rows in a sub-selection and filtering out my results by IDs that appear that many times works, but It's really ugly.
There HAS to be a way to do this without explicitly count()ing rows. I hope.
Not an answer to your question, but a general improvement.
I'd recommend using JOIN syntax to join your tables together.
This would change your query to be:
SELECT Agents.aid
FROM Agents
INNER JOIN Orders
ON Agents.aid = Orders.aid
INNER JOIN Customers
ON Customers.cid = Orders.cid
WHERE Customers.city='Duluth'
GROUP BY Agents.aid
HAVING count(Agents.aid) > 1
What variant of SQL are you using?
To start with, you can (and should) use JOIN instead of doing it in the WHERE clause, e.g.,
select Agents.aid
from Agents
join Orders on Agents.aid = Orders.aid
join Customers on Customers.cid = Orders.cid
where Customers.city = 'Duluth'
group by Agents.aid
having count(Agents.aid) > 1
After that, I'm afraid I might be a little lost. Using the table names in your example query, what (in English, not pseudocode) are you trying to retrieve? For example, I think your sample query is retrieving the PK for all Agents that have been involved in at least 2 Orders involving Customers in Duluth.
Also, some table definitions for Agents, Orders, and Customers might help (then again, they might be irrelevant).
I'm not sure if I understood you problem, but I think the following query is what you want:
SELECT *
FROM customers b
INNER JOIN orders c USING (cid)
WHERE b.city = 'Duluth'
AND NOT EXISTS (SELECT 1
FROM customers b2
WHERE b2.city = b.city
AND b2.cid <> cid);
Probably you will need some indexes on these columns.