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-- Scalar UDF Example

-- We will create a function to provide a more 

-- descriptive result set for the EmailPromotion column

-- in the Person.EmailAddress table

SELECT * FROM Person.Person

-- Create a function named fnEmailPromo

-- It will accept EmailAddress as an input and

-- return a string value based on the int value

-- being passed in

-- We will use the function in a select statement

CREATE FUNCTION fnEmailPromo (@promo int)

RETURNS varchar(20)

AS

BEGIN

DECLARE @ret_promo varchar(20)

select @ret_promo=

	CASE 

		WHEN @promo=0 then 'None'

		WHEN @promo=1 then 'Local'

		WHEN @promo=2 THEN 'National'

		ELSE 'Not designated'

	END

	RETURN @ret_promo

END

-- Now, let's user our new fnEmailPromo function

-- Note that to call the new function we must include

-- dbo. in the name

SELECT FirstName + ' ' + Lastname Customer, dbo.fnEmailPromo(EmailPromotion) 'Promotion Type'

FROM Person.Person

-- TVF Example

-- Here are the three tables we will be getting our data from

select top 1 * from person.person

select top 1 * from person.emailaddress

select top 1 * from humanresources.employee

-- Our TVF will return the names and email addresses of our

-- employees based on their gender

-- Let's create our TVF

CREATE FUNCTION dbo.fnGetEmail(@gender char(1))

RETURNS TABLE

AS

RETURN

	SELECT p.FirstName, p.Lastname,e.EmailAddress,em.Gender

	FROM person.person p

	JOIN person.EmailAddress e on p.BusinessEntityID=e.BusinessEntityID

	JOIN HumanResources.Employee em on e.BusinessEntityID=em.BusinessEntityID

	WHERE em.Gender=@gender

-- Let's use our TVF

SELECT * FROM dbo.fnGetEmail('m')

-- We can add a WHERE clause to get more creative with the results

SELECT * FROM dbo.fnGetEmail('m')

WHERE LastName LIKE 'D%'

--Correlated Subquery

--First let's look at a join query

SELECT DISTINCT p.BusinessEntityID, p.FirstName + ' ' + p.LastName Name

FROM

Person.Person p

JOIN

sales.SalesOrderHeader s

ON

p.BusinessEntityID=s.SalesPersonID

WHERE s.TotalDue>150000

--Now, let's write this as a correlated subquery

--NOTE that the inner query runs first and locates a matching record

--The outer query runs using the record found, then the inner query 

--runs again searching for another match...until all records are found

SELECT p.BusinessEntityID, FirstName + ' ' + LastName Salesperson FROM Person.Person p

WHERE

EXISTS

	(SELECT s.SalesPersonID FROM Sales.Salesorderheader s 

	 WHERE TotalDue>150000

	 and p.BusinessEntityID=s.SalesPersonID)

-- Multi-vaued query examples

-- Let's start off with a simple multi-valued query

-- that returns a list of values

-- We need a list of employees who were born after 1972

-- Here' where we can get the data...

SELECT TOP 1 * from Person.Person

SELECT TOP 1 * from HumanResources.Employee

-- We can use a subquery to pull the list of BusinesEntityID's

-- for every BirthDate greater than 1972 in the Employee table

-- and use that list with the IN keyword to get the Employee names

-- from the Person table

SELECT Firstname + ' ' + Lastname Employee

FROM Person.Person

WHERE Person.BusinessEntityID IN

	(SELECT BusinessEntityID

	 FROM HumanResources.Employee

	 WHERE Year(BirthDate)>1972)

ORDER BY LastName, FirstName

-- Now, let's use a table-value subquery...also known as a table expression

-- to find the last SalesOrderID for each year

SELECT OrderYear, MAX(SalesOrderID) LastOrderID

FROM

	(SELECT SalesOrderID, Year(OrderDate) OrderYear -- Run this inner query separately 

	 FROM Sales.SalesOrderHeader)as D               -- to see the table being returned

GROUP BY OrderYear 

ORDER BY OrderYear