Answer simple quiz at the end of the blog post and –
Every day one winner from India will get Joes 2 Pros Volume 2.
Every day one winner from United States will get Joes 2 Pros Volume 2.
Many to Many relationships
If anyone has done some shopping on the internet you are familiar with the term “Shopping Cart” or “Shopping basket”. After you have selected a product you want to buy the storefront will gladly let you keep on shopping until there are many items in you shopping cart. On my last trip to Amazon.com I put 3 things in my cart before checking out. One item was a HDMI cable box converter for my flat screen TV at home. I took a closer look at this products rating and reviews before buying. Below this product it said this items was in the top 100 selling items in home electronics. This means this items has sold to more people than just me and I was not the first to buy this product.
Based on the story above what is the relationship to a product (like the HDMI cable box) and a customer who may want to buy that item? As a customer I can buy many products at once in my shopping cart. Does this mean there is a one to many relationship between customers (like me) and products (like the HDMI cable box). Yes there is but that is only a half truth. A product like the HDMI cable box can be purchased by many different customers. Therefore there is a Many to Many relationship between Customers and products. This product can be bought by many customers and many customer can buy this product.
Another many to many relationship is between books and Authors. I have written 5 books so we know there is at least a one to many relationship between Authors and Books. Now look at my 4th book (SQL Programming Joes 2 Pros Volume 4 – ISBN-13: 978-1451579482). This book has two authors (Rick A. Morelan and Pinal Dave). Since an Author can write many books and a book can be written by many authors there is a many to many relationship between authors and books.
We need a new process to map this complex relationship. Sometimes tables exist for the sole purpose of allowing indirect relationships between tables. What do you call tables the handle relationships for other tables? Common terms for these type of tables are mapping tables, bridge tables, or junction tables.
Many to Many relationships with invoicing systems
As discussed earlier a product can appear on many invoices and an invoice can have many products. The relationship between products and invoices is known as a many-to-many relationship as seen in the figure below.
If you were to ask yourself “What Products are on Invoice 5631?” or “Go-Duck was ordered on how many invoices?” you could resolve this query? The Figure below shows us how to resolve both mappings. We can see the Go-Duck toy was order twice (on 7/15 and on 9/22). We can also see the shopping cart 5631 has two items in it (Toy Car and Furchee).
Now we’ll take a look at many-to-many relationships between sales invoices and products in the JProCo sample database.
Here is an example of JProCo’s sales invoices mapping to a bridge table (SalesInvoiceDetail) in order to map over to the CurrentProducts table. The CurrentProducts table gives us all the detail of the current products that have been ordered.
With SalesInvoice 5 It looks like many products were ordered on that one invoice (Products 9, 11, 12, and 16). To see what those products are, we would look over to the CurrentProducts table. We see Product 9 is an Underwater Tour 3 Days East Coast. Product 11 is an Underwater Tour 1 Week East Coast, and so forth. So a SalesInvoice can have many products, and products can be ordered on multiple sales invoices.
The SalesInvoiceDetail table is the mapping table that is handling the many to many relationship between the SalesInvoice table and the CurrentProducts table. This 3 table join between these tables would look like the query you see below.
SELECT si.CustomerID, si.InvoiceID, si.OrderDate,
sd.Quantity, cp.ProductName, cp.RetailPrice
FROM dbo.SalesInvoiceDetail AS sd
INNER JOIN dbo.SalesInvoice AS si
ON sd.InvoiceID = si.InvoiceID
INNER JOIN CurrentProducts AS cp
ON cp.ProductID = sd.ProductID
Note: If you want to setup the sample JProCo database on your system you can watch this video. For this post you will want to run the SQLQueriesChapter3.0Setup.sql script from Volume 2.
Question 8
Q.8) You have tables named dbo.SalesInvoice and dbo.SalesInvoiceDetail. CustomerID is located in the SalesInvoice table and InvoiceID is located in both tables. You have been told to show the discount amounts from the SalesInvoiceDetail table that correspond to the sales of a specific CustomerID of 490. Which T-SQL statement should you use?
- SELECT sd.CustomerID, si.DiscountAmt, cp.ProductName
FROM dbo.SalesInvoiceDetail sd
INNER JOIN dbo.SalesInvoice si
ON sd.InvoiceID= si.InvoiceID
INNER JOIN CurrentProducts AS cp
ON cp.ProductID = sd.ProductID
WHERE si.CustomerID= 490 - SELECT sd.CustomerID, si.DiscountAmt, cp.ProductName
FROM dbo.SalesInvoiceDetail sd
INNER JOIN CurrentProducts AS cp
ON cp.ProductID = sd.ProductID
WHERE si.CustomerID= 490 - SELECT sd.CustomerID, si.DiscountAmt, cp.ProductName
FROM dbo.SalesInvoiceDetail sd
WHERE EXISTS (dbo.SalesInvoice si
ON sd.InvoiceID= si.InvoiceID
INNER JOIN CurrentProducts AS cp
ON cp.ProductID = sd.ProductID
WHERE si.CustomerID= 490)
Please post your answer in comment section to win Joes 2 Pros books.
Rules:
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Winner from United States will get Joes 2 Pros Volume 2.
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The contest is open till next blog post shows up at which is next day GTM+2.5.
Reference: Pinal Dave (https://blog.sqlauthority.com)
123 Comments. Leave new
This is a very interesting and tricky question, as none of the answers is correct. I spent about 5 or more minutes looking at these 3 queries before coming to this conclusion.
Answer #3 can be eliminated right away as the syntax is wrong.
Answer #2 can be eliminated also as it doesn’t reference SalesInvoice table at all
Finally, answer #1 is almost correct, but it references sd.CustomerID, which is wrong as CustomerID belongs to SalesInvoice table. Therefore none of the answers is correct.
So, my answer will be:
SELECT si.CustomerID, sd.DiscountAmt, cp.ProductName
FROM dbo.SalesInvoiceDetail sd
INNER JOIN dbo.SalesInvoice si
ON sd.InvoiceID= si.InvoiceID
INNER JOIN CurrentProducts AS cp — if we need to show Product Names we join with CurrentProducts table
ON cp.ProductID = sd.ProductID
WHERE si.CustomerID= 490
It’s the same as #1 with the corrected typo.
I am from USA
I think the alias is wrong in the first option’s query but if I have to go with given options then I assume that “CustomerID” is also present in dbo.SalesInvoiceDetail table.
So, the correct answer is option (1).
Thank You.
Country – India.
Hi,
the Answer is 1.
SELECT sd.CustomerID, si.DiscountAmt, cp.ProductName
FROM dbo.SalesInvoiceDetail sd
INNER JOIN dbo.SalesInvoice si
ON sd.InvoiceID= si.InvoiceID
INNER JOIN CurrentProducts AS cp
ON cp.ProductID = sd.ProductID
WHERE si.CustomerID= 490
We can inner join the tables to get the required fields and filter it by the alias name of table.
SivaSakthiVel
– INDIA
“Save Our tigers”
#1 is the correct answer–SELECT sd.CustomerID, si.DiscountAmt, cp.ProductName
FROM dbo.SalesInvoiceDetail sd
INNER JOIN dbo.SalesInvoice si
ON sd.InvoiceID= si.InvoiceID
INNER JOIN CurrentProducts AS cp
ON cp.ProductID = sd.ProductID
WHERE si.CustomerID= 490
Rahul Thapa–India
Option 1 will return an invalid column
Option 2 does not join to a table that contains the CustomerId
Option 3 is not valid.
Option 1 is the closest in that it has the correct joins, but needs to have the select statement edited as follows:
SELECT si.CustomerID, sd.DiscountAmt, cp.ProductName
FROM dbo.SalesInvoiceDetail sd
INNER JOIN dbo.SalesInvoice si
ON sd.InvoiceID= si.InvoiceID
INNER JOIN CurrentProducts AS cp
ON cp.ProductID = sd.ProductID
WHERE si.CustomerID= 490
Thanks for the fun question. I’m from the USA.
Mike
Hi Sir,
As per the question you have said that “CustomerID is located in the SalesInvoice table”
but in all the queries the select statement is like
“SELECT sd.CustomerID, si.DiscountAmt, cp.ProductName
FROM dbo.SalesInvoiceDetail sd”
so as per this all the queries will fail.
If that was a mistake done while typing then answer 1 is the correct option.
i.e “SELECT si.CustomerID, si.DiscountAmt, cp.ProductName
FROM dbo.SalesInvoiceDetail sd
INNER JOIN dbo.SalesInvoice si
ON sd.InvoiceID= si.InvoiceID
INNER JOIN CurrentProducts AS cp
ON cp.ProductID = sd.ProductID
WHERE si.CustomerID= 490”
Anish Shenoy
INDIA,Bangalore,Karnataka
Hi Sir
I’ll use option number one to run this t-sql
1.SELECT sd.CustomerID, si.DiscountAmt, cp.ProductName
FROM dbo.SalesInvoiceDetail sd
INNER JOIN dbo.SalesInvoice si
ON sd.InvoiceID= si.InvoiceID
INNER JOIN CurrentProducts AS cp
ON cp.ProductID = sd.ProductID
WHERE si.CustomerID= 490
Leonardo Guerrero
from Chile
answer:
1.SELECT sd.CustomerID, si.DiscountAmt, cp.ProductName
FROM dbo.SalesInvoiceDetail sd
INNER JOIN dbo.SalesInvoice si
ON sd.InvoiceID= si.InvoiceID
INNER JOIN CurrentProducts AS cp
ON cp.ProductID = sd.ProductID
WHERE si.CustomerID= 490
lalit
india
Answer is option 1
Sandeep
INDIA
1.SELECT sd.CustomerID, si.DiscountAmt, cp.ProductName
FROM dbo.SalesInvoiceDetail sd
INNER JOIN dbo.SalesInvoice si
ON sd.InvoiceID= si.InvoiceID
INNER JOIN CurrentProducts AS cp
ON cp.ProductID = sd.ProductID
WHERE si.CustomerID= 490
Gordon Kane
Allen TX
USA
Answer 1 is correct:
“SELECT sd.CustomerID, si.DiscountAmt, cp.ProductName
FROM dbo.SalesInvoiceDetail sd
INNER JOIN dbo.SalesInvoice si
ON sd.InvoiceID= si.InvoiceID
INNER JOIN CurrentProducts AS cp
ON cp.ProductID = sd.ProductID
WHERE si.CustomerID= 490”
Rajneesh Verma
(INDIA)
Answer
1. SELECT sd.CustomerID, si.DiscountAmt, cp.ProductName
FROM dbo.SalesInvoiceDetail sd
INNER JOIN dbo.SalesInvoice si
ON sd.InvoiceID= si.InvoiceID
INNER JOIN CurrentProducts AS cp
ON cp.ProductID = sd.ProductID
WHERE si.CustomerID= 490
Thank You
Ramdas
Hello,
Find my answer below :
2nd and 3rd option is wrong. if we consider 1st option then it will give an error message like “Invalid column name si.DiscountAmt” .
If we rectify the 1st option query by modifying si.DiscountAmt to sd.DiscountAmt. then it will give you error free output.
Hope you understand…
I am from India..
OPTION 1 IS THE CORRECT ANSWER
RAHUL SINGH RATHORE
INDIA
Correct Answer for the above question is Option : 1.
SELECT sd.CustomerID, si.DiscountAmt, cp.ProductName
FROM dbo.SalesInvoiceDetail sd
INNER JOIN dbo.SalesInvoice si
ON sd.InvoiceID= si.InvoiceID
INNER JOIN CurrentProducts AS cp
ON cp.ProductID = sd.ProductID
WHERE si.CustomerID= 490
DILIP KUMAR JENA
Country : INDIA
As you said : “CustomerID is located in the SalesInvoice table and InvoiceID is located in both tables. You have been told to show the discount amounts from the SalesInvoiceDetail table that correspond to the sales of a specific CustomerID of 490. Which T-SQL statement should you use? ”
So Query should be :
SELECT si.CustomerID, sd.DiscountAmt, cp.ProductName
FROM dbo.SalesInvoiceDetail sd INNER JOIN dbo.SalesInvoice si
ON sd.InvoiceID= si.InvoiceID
INNER JOIN CurrentProducts AS cp ON cp.ProductID = sd.ProductID
WHERE si.CustomerID= 490
Correct answer is :
1.SELECT sd.CustomerID, si.DiscountAmt, cp.ProductName
FROM dbo.SalesInvoiceDetail sd
INNER JOIN dbo.SalesInvoice si
ON sd.InvoiceID= si.InvoiceID
INNER JOIN CurrentProducts AS cp
ON cp.ProductID = sd.ProductID
WHERE si.CustomerID= 490
Country: United States
The (most) correct option is 1:
SELECT sd.CustomerID, si.DiscountAmt, cp.ProductName
FROM dbo.SalesInvoiceDetail sd
INNER JOIN dbo.SalesInvoice si
ON sd.InvoiceID= si.InvoiceID
INNER JOIN CurrentProducts AS cp
ON cp.ProductID = sd.ProductID
WHERE si.CustomerID= 490
Option2 -> doesn’t join against salesinvoice which contains the customer ID
Option3 -> is not a valid statement
Country of Residence: USA
Option 1
SELECT sd.CustomerID, si.DiscountAmt, cp.ProductName
FROM dbo.SalesInvoiceDetail sd
INNER JOIN dbo.SalesInvoice si
ON sd.InvoiceID= si.InvoiceID
INNER JOIN CurrentProducts AS cp
ON cp.ProductID = sd.ProductID
WHERE si.CustomerID= 490
USA
1. SELECT sd.CustomerID, si.DiscountAmt, cp.ProductName
FROM dbo.SalesInvoiceDetail sd
INNER JOIN dbo.SalesInvoice si
ON sd.InvoiceID= si.InvoiceID
INNER JOIN CurrentProducts AS cp
ON cp.ProductID = sd.ProductID
WHERE si.CustomerID= 490