Defining parameters in table valued function - SQL Server - sql-server

Question

I am trying to return matching zip codes as a table, so I can use it with 'Where zipCode IN(...) statement.
create function dbo.zipSearch(#zip varchar(12), #mile int)
returns table
as
begin
declare #ns float = #mile * 0.00569;
declare #ew float = #mile * 0.01629;
declare #ltt float, #lng float;
Select #ltt = latitude, #lng = longitude From ZipCode Where ZIP = #zip;
Select ZIP From zipcode Where latitude >= #ltt - #ns and latitude <= #ltt + #ns and longitude >= #lng - #ew and longitude <= #lng + #ew;
return
end
What would be the alternative if this is not possible?

Answer 1

Here is how you could turn this into an inline table valued function. The performance benefits might surprise you.
create function dbo.zipSearch(#zip varchar(12), #mile int)returns table as return
Select ZIP
From zipcode
cross apply
(
select latitude
, longitude
from ZipCode
where Zip = #zip
) LatLong
Where latitude >= LatLong.latitude - (#mile * 0.00569)
and latitude <= LatLong.latitude + (#mile * 0.00569)
and longitude >= LatLong.longitude - (#mile * 0.01629)
and longitude <= LatLong.longitude + (#mile * 0.01629);
Here are just a few articles about the differences.
Multi-statement Table Valued Function vs Inline Table Valued Function
http://www.sqlservercentral.com/blogs/discussionofsqlserver/2012/02/15/comparing-inline-and-multistatement-table-valued-functions/
http://sqlmag.com/t-sql/inline-vs-multistatement-table-valued-udfs

Answer 2

Posting the final version of the function in case someone else hits the same wall as I do. Thanks to #Tab Alleman for the tip. It was a syntax issue.
create function dbo.zipSearch(#zip varchar(12), #mile int)
returns #tmp TABLE (zipCode varchar(12))
as
begin
declare #ns float = #mile * 0.00569;
declare #ew float = #mile * 0.01629;
declare #ltt float, #lng float;
Select #ltt = latitude, #lng = longitude From ZipCode Where ZIP = #zip;
INSERT #tmp
Select ZIP From zipcode Where latitude >= #ltt - #ns and latitude <= #ltt + #ns and longitude >= #lng - #ew and longitude <= #lng + #ew;
return
end