I am trying to write a query in db2 for a database that has books and the customers who bought them and I am to find the pairs of customers who bought common books.
Say for example the DB is called "DB" and it looks like this
CustomerID Book Cost
1 Harry Potter 12
2 SOUE 6
3 Harry Potter 12
4 Harry Potter 12
5 SOUE 6
6 SOUE 6
I am basically trying to get the resulting table look like
Customer1 Customer2
1 3
1 4
2 5
2 6
I have tried using group by's but I cant seem to get the idea right
I've tried
Select book
from DB
group by book
which uniquely gives me all the books but I don't know how I would go about getting the customer pairs. Any help would be greatly appreciated thank you.
I'd self-join according to the book column. In order to avoid conceptual duplicates (e.g., 1-3 and 3-1), you could make an arbitrary decision to always display the lower customer ID on the left:
SELECT DISTINCT a.customerid, b.customerid
FROM mytable a
JOIN mytable b ON a.book = b.book AND a.customerid < b.customerid
EDIT:
To answer the question in the comments, if you want to display customer names instead of ids, you'd need to join the customers table to this query, twice, once for each column:
SELECT DISTINCT ca.name AS customer1, cb.name AS customer2
FROM purchases pa
JOIN purchases pb ON pa.book = pb.book AND pa.customerid < pb.customerid
JOIN customers ca ON pa.customer_id = ca.id
JOIN customers cb ON pb.customer_id = cb.id
Related
Newbie question about joining tables. I want to retrieve a name from a column TWICE in a SQL statement, and I'm running in circles.
I Have two Tables - "Company" & "People"
Table -"People"
ID
Name
Phone
1
Luke
555-1212
2
Leia
555-1234
3
Han
999-8888
4
Anikin
888-9876
5
Obi-wan
555-1212
6
R2-D2
#% - **!?
Table - "Company"
ID
CompanyName
PrimaryContact
AltContact
1
Speeders R Us
5
1
2
Droid Repair World
6
4
3
Luke's Second Hand Store
1
4
4
Cloak World
4
5
5
Ye Old Blaster Shoppe
3
2
If I want to get a result that gives BOTH the Contact Names for a Company, How would I do it?
I can get the PrimaryContact to JOIN Properly using something like...
SELECT C.*, P.Name as 'Primary'
FROM `Company` C
Join People P on
C.PrimaryContact = P.ID
WHERE C.ID =3
which successfully returns
ID
CompanyName
PrimaryContact
AltContact
Primary
3
Luke's Second Hand Store
1
4
Luke
But for the life of me, I can't figure out how to modify this SQL to also return "Anikin" as the Alternate Contact. Is this an example of where a UNION statement would help?
You can join to the same table multiple times, just give a new alias every time.
Join People P on C.PrimaryContact = P.ID
Join People P1 on C.AltContact = P1.ID
Join People altcontact on C.AltContact = altcontact.ID
Join People P256 on C.yetanotheralternateContact = P256.ID
You need to to join for ecervy contact another Persons table
SELECT C.ID,C.CompanyName, P.Name as 'Primary' , P.Phone As 'primary_Phone', P2.Name on 'Alternative', P2.Phone as 'Alternatibe_Phone
FROM `Company` C
Join People P on
C.PrimaryContact = P.ID
Join People P2 on
C.AltContact = P2.ID
WHERE C.ID
thanks in advance for any help on this, I am a bit of a newbie to MS SQL and I want to do something that I think is achievable but don't have the know how.
I have a simple table called "suppliers" where I can do (SELECT id, name FROM suppliers ORDER BY id ASC)
id
name
1
ACME
2
First Stop Business Supplies
3
All in One Supply Warehouse
4
Farm First Supplies
I have another table called "products"
id
name
supplier_id
1
Item 1
2
2
Item 2
1
3
Item 3
1
4
Item 4
3
5
Item 5
2
I want to list all the suppliers and get the total amount of products for each supplier if that makes sense on the same row? I am just not sure how to pass the suppliers.id through the query to get the count.
I am hoping to get to this:
id
name
total_products
1
ACME
2
2
First Stop Business Supplies
2
3
All in One Supply Warehouse
1
4
Farm First Supplies
0
I really appreciate any help on this.
Three concepts to grasp here. Left Join, group by, and Count().
select s.id, s.name, Count(*) as total_products
from suppliers s
left join products p on s.id=p.supplier_id --the left join gets your no matches
group by s.id, s.name
left join is a join where all of the values from the first table are kept even if there are no matches in the second.
Group by is an aggregation tool where the columns to be aggregated are entered.
Count() is simply a count of transactions for the grouped columns.
Try this :-
SELECT id, name, C.total_products
FROM Suppliers S
OUTER APPLY (
SELECT Count(id) AS total_products
FROM Products P
WHERE P.supplier_id = S.id
) C
We have a situation in which one part of our stored procedure need to be filled with a join query, which had multiple filters in it. We need a solution only with join (it is easy to implement in the subquery, but our situation demands it to be a join [since the procedure has a where clause followed by it] )
We have two tables Customer and Order. We need to exclude the rows of Customer table, if Customer_id is present Order table & order_code = 10 & Customer.Grade = 3. It is not mandatory for all Customer_id to be present in Order table, but we still need it in the final result.
Customer Table OrderTable
Customer_id Grade Customer_id order_code
1 3 1 10
2 3 1 40
3 2 2 50
4 3 3 30
*Multiple Customer_id can be present in the OrderTable
Expected result :
Customer_id Grade
2 3
3 2
4 3
I think this may be what you need, not sure I understand the question properly.
select c.id, c.grade
from customer c left join customer_order o on (c.id = o.customer_id and o.order_code <> 10)
where c.grade = 3
This should give you all customers with a Grade of 3 that also have orders, provided the order_code is not 10. If you want to show customers that do not have any orders also, make it a left join.
You can express the logic like this:
select c.*
from customers c
where not (grade = 3 and
exists (select 1
from orders o
where o.customer_id = c.customer_id and
o.order_code = 10
)
);
I know this must have been answered before here, but I simply can't find a matching question.
Using a LIKE '%keyword%', I want to search a many-to-many data relationship in a MSSQL database and reduce it to a one-to-one result set. The two tables are joined through a linking table. Here's a very simplified version of what I'm talking about:
Books:
book_ id title
1 Treasure Island
2 Poe Collected Stories
3 Invest in Treasure Islands
Categories:
category_id name
1 Children
2 Adventure
3 Horror
4 Classic
5 Money
BookCategory:
book_id category_id
1 1
1 2
1 4
2 3
2 4
3 5
What I want to do is search for a phrase in the title (e.g. '%treasure island%') and get matching Books records that contain the search string and the single highest matching Categories record that goes with each book -- I want to discard the lesser category records. In other words, I'm looking for this:
book_id title category_id name
1 Treasure Island 4 Classic
3 Invest in Treasure Islands 5 Money
Any suggestions?
Try this. Filter your lookup table, then join:
With maxCategories AS
(select book_id, max(category_id) as category_id from BookCategory group by book_id)
select Books.book_id, Books.Title, Categories.category_id, Categories.name
from Books
inner join maxCategories on (Books.book_id = maxCategories.book_id)
inner join Categories on (Categories.category_id = maxCategories.category_id)
where Books.title like '%treasure island%'
Try:
select * from
(select b.*,
c.*,
row_number() over (partition by bc.book_id
order by bc.category_id desc) rn
from Books b
join BookCategory bc on b.book_id = bc.book_id
join Categories c on bc.category_id = c.category_id
where b.name like '%treasure island%') sq
where rn=1
Ok I have two tables.
Table IDAssoc has the columnsbill_id, year, area_id.
Table Bill has the columns bill_id, year, main_id, and amount_due.
I'm trying to get the sum of the amount_due column from the bill table for each of the associated area_ids in the IDAssoc table.
I'm doing a select statement to select the sum and joining on the bill_ids. How can I set this up so it will have a single row for each of the associated bills in each area_id from the assoc table. There may be three or four bill_ids associated with each area_id and I need those summed for each and returned so I can use this select in another statement. I have a group by set up for the area_id but it still is returning each row and not summing them up for each area_id. I have the year and main_id specified already in the where clause to return the data that I want, but I can't get the sum to work properly. Sorry I'm still learning and I'm not sure how to do this. Thanks!
Edit- Basically the query I'm trying so far is basically just like the one posted below:
select a.area_id, sum(b.amount_due)
from IDAssoc a
inner join Bill b
on a.bill_id = b.bill_id
where Bill.year = 2006 and bill.bill_id = 11111
These are just arbitrary numbers.
The data this is returning is like this:
amount_due - area_id
.05 1003
.15 1003
.11 1003
65 1004
55 1004
I need one row returned for each area_id with the amount_due summed. The area_id is only in the assoc table and not in the bill table.
select a.area_id, sum(b.amount_due)
from IDAssoc a
inner join Bill b
on a.bill_id = b.bill_id
where b.year = 2006 and b.bill_id = 11111
group by a.area_id
You might want to change inner join to left join if one IDAssoc can have many or no Bill:
select a.area_id, coalesce(sum(b.amount_due),0)
from IDAssoc a
left join Bill b
on a.bill_id = b.bill_id
where b.year = 2006 and b.bill_id = 11111
group by a.area_id
You are missing the GROUP BY clause:
SELECT a.area_id, SUM(b.amount_due) TotalAmount
FROM IDAssoc a
LEFT JOIN Bill b
ON a.bill_id = b.bill_id
GROUP BY a.area_id