W3. SQL Inner Join

Question 1

Q: What does the INNER JOIN keyword do?

Answer 1

A: It selects records with matching values in both tables.

Question 2

Q: Write a query to join Products and Categories on CategoryID to select ProductID, ProductName, and CategoryName.

Answer 2

SELECT ProductID, ProductName, CategoryName
FROM Products
INNER JOIN Categories ON Products.CategoryID = Categories.CategoryID;

Question 3

Q: What happens to records without a match in an INNER JOIN?

Answer 3

A: They are not returned in the result.

Question 4

Q: What is the syntax for using INNER JOIN?

Answer 4

SELECT column_name(s)
FROM table1
INNER JOIN table2
ON table1.column_name = table2.column_name;

Question 5

Q: Why is it good practice to specify table names when using JOIN?

Answer 5

A: To avoid ambiguity, especially when columns with the same name exist in both tables.

Question 6

Q: Write a query that specifies table names to join Products and Categories on CategoryID.

Answer 6

SELECT Products.ProductID, Products.ProductName, Categories.CategoryName
FROM Products
INNER JOIN Categories ON Products.CategoryID = Categories.CategoryID;

Question 7

Q: Are JOIN and INNER JOIN equivalent?

Answer 7

A: Yes, INNER JOIN is the default, so JOIN without INNER has the same effect.

Question 8

Q: Write an example query using JOIN (without INNER) to join Products and Categories.

Answer 8

SELECT Products.ProductID, Products.ProductName, Categories.CategoryName
FROM Products
JOIN Categories ON Products.CategoryID = Categories.CategoryID;

Question 9

Q: Can you JOIN more than two tables? If yes, how?

Answer 9

A: Yes, by joining additional tables in sequence using INNER JOIN with relevant keys.

Question 10

Q: Write a query to join Orders, Customers, and Shippers to select OrderID, CustomerName, and ShipperName.

Answer 10

SELECT Orders.OrderID, Customers.CustomerName, Shippers.ShipperName
FROM ((Orders
INNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID)
INNER JOIN Shippers ON Orders.ShipperID = Shippers.ShipperID);