How to call function in update statement - tsql

Question

I can get the first, middle, last name for a function passing a string. How do I pass the element in the query to the function for an update statement.
--test update logic, and name parsing
USE PCUnitTest
UPDATE p
SET --Need FIRST_NAME, MIDDLE_NAME, LAST_NAME
p.FIRST_NAME = SELECT forename FROM (SELECT * FROM dbo.NameParser(c.CONTACT)) AS FirstName, --shows multipart identifier could not be bound
p.FIRST_NAME = SELECT forename FROM (SELECT * FROM dbo.NameParser('Andy D Where')) AS FirstName, --returns Andy
p.MIDDLE_NAME = SELECT middle_name FROM (SELECT * FROM dbo.NameParser('Andy D Where')) AS MiddleName, --returns D
p.LAST_NAME = SELECT surname FROM (SELECT * FROM dbo.NameParser('Andy D Where')) AS LastName --returns Where
FROM GMUnitTest.dbo.CONTACT1 c
JOIN PCUnitTest.dbo.PEOPLE p
ON p.PEOPLE_ID = c.KEY4
WHERE c.Key1 = '76'; --Test with a current string
GO

Answer 1

I think you mean to do something similar to this:
USE PCUnitTest
GO
UPDATE P
SET
P.First_Name = T.ForeName
,P.Middle_Name = T.Middle_Name
,P.Last_name = T.Surname
FROM GMUnitTest.dbo.Contact1 C
INNER JOIN PCUnitTest.dbo.People P
ON P.People_ID = C.Key4
CROSS APPLY dbo.NameParser(C.Contact) T
WHERE C.Key1 = '76'
;
I don't know what you're using to parse the names, but I can see that it always returns the first name, middle name, and last name. You might want to consider adding an extra input parameter to your function so that you can specifically request the first, middle, or last name by entering a numerical (or other) parameter.
In the query up above, each name would return duplicate results, so you would probably end up running an UPDATE against the same value a few times, each time with the same value.
By adding another parameter to your function, you could use CROSS APPLY several times (or OUTER APPLY if there's a chance that one or more monikers are missing) in order to update more efficiently, as such:
USE PCUnitTest
GO
UPDATE P
SET
P.First_Name = FirstName.ForeName
,P.Middle_Name = MiddleName.Middle_Name
,P.Last_name = LastName.Surname
FROM GMUnitTest.dbo.Contact1 C
INNER JOIN PCUnitTest.dbo.People P
ON P.People_ID = C.Key4
CROSS APPLY dbo.NameParser(C.Contact,1) FirstName
CROSS APPLY dbo.NameParser(C.Contact,2) MiddleName
CROSS APPLY dbo.NameParser(C.Contact,3) LastName
WHERE C.Key1 = '76'
;