TSQL Subquery effeciency - sql-server

Question

I am trying to write a subquery in a view to be returned as a column but I am not exactly sure what would give me the most efficient call.
I have View A that gathers a bunch of fields from different tables (one table being Listings that has has a 1 to many relationship with OpenHours) then one of the fields I want it to be from another table (OpenHours) that will only be Today's Open hours field.
The OpenHours table has ListingID, Day (0 based for the day of the week), Hours (text of the open hours such as "8:00am-5:00pm"). Here is what I need to do:
Check if OpenTable has a record for that particular listing that day = 7, if its 7 (which is not a day of the week) then return "Open 24 hours".
If does not exist then return the next record, since SQL Servers datepart(dw.. is 1 based, following will be used select datepart(dw,getdate())-1 to get a 0 day based day of week starting on Sunday (Sunday being 0)
Return nothing if no records exist that match the criteria.
I would appreciate some help on this. I attempted to write this but could not get far. I am not sure how to declare variables for day of the week in the view.
UPDATE
here is my function, anyone see any glaring inefficiencies?
ALTER FUNCTION [dbo].[GetTodaysOpenHours](#ListingID int)
RETURNS VARCHAR(50)
AS
BEGIN
DECLARE #DayOfWeek int
--SQL Day of week starts on sunday but it is 1 based, listing open hours are 0 based
SET #DayOfWeek = DATEPART(DW, GETDATE()) - 1
DECLARE #OpenHours VARCHAR(50)
IF EXISTS(SELECT * FROM OpenHours WHERE Day = 7 AND ListingID = #ListingID)
SET #OpenHours = 'Open 24 Hours'
ELSE
SELECT #OpenHours = Hours FROM OpenHours WHERE ListingID = #ListingID AND Day = #DayOfWeek
RETURN #OpenHours
END
UPDATED VIEW
ALTER view [dbo].[vListings]
as
SELECT l.ListingID, l.ExpiryDate, l.IsApproved, l.IsActive, l.Position,MoneyField1, DateField1,
IntField1, IntField2, IntField3, IntField4,
BoolField1, BoolField2, BoolField3,
OptionField1, OptionField2, OptionField3, OptionField4,
IsTop, TopStartDate, TopExpireDate, Address, Address + ' ' + c.Name + ' ' + p.Name AS FullAddress,
o1.Description as Options1Description,
o2.Description as Options2Description,
o3.Description as Options3Description,
o4.Description as Options4Description,
COALESCE(
(SELECT TOP 1 ThumbnailPath
FROM Attachments
WHERE ListingID = l.listingID), '/content/images/noImageThumbnail2.jpg') AS MainThumbnail,
COALESCE(
(SELECT TOP 1 ThumbnailPath2
FROM Attachments
WHERE ListingID = l.listingID), '/content/images/noImageThumbnail.jpg') AS MainThumbnail2,
l.UserID,
c.SubDomainName as CitySubDomainName, l.Name,
CASE
WHEN l.IsAutoGenerated = 1 THEN l.ImportedPhoneNumber
ELSE dbo.FormatPhoneNumber(u.PhoneNumber)
END as PhoneNumber,
CASE
WHEN l.IsAutoGenerated = 1 THEN l.ImportedContactInfo
ELSE u.FirstName + ' ' + u.LastName
END as ContractInfo,
p.Abbv as StateAbbv,
cn.Code as CountryCode,
l.Comments, l.UniqueID, l.Rating, l.Website,
(select L.ListingID,
isnull(H1.Hours, H2.Hours) as Hours
from Listings L
outer apply (
select Hours FROM OpenHours H WHERE H.Day = 7
AND H.ListingID = L.ListingID
) H1
outer apply (
select Hours FROM OpenHours H WHERE Day = DATEPART(DW, GETDATE()) - 1
AND H.ListingID = L.ListingID
) H2
--dbo.GetTodaysOpenHours(l.ListingID) as TodaysOpenHours
FROM Listings l
INNER JOIN Cities c ON c.CityID = l.CITYID
INNER JOIN Provinces p ON p.ProvinceID = c.ProvinceID
INNER JOIN Countries cn ON cn.CountryID = p.CountryID
INNER JOIN AspNetUsers u ON u.Id = l.UserID
LEFT OUTER JOIN Options1 o1 ON o1.OptionID = l.OptionField1
LEFT OUTER JOIN Options2 o2 ON o2.OptionID = l.OptionField2
LEFT OUTER JOIN Options3 o3 ON o3.OptionID = l.OptionField3
LEFT OUTER JOIN Options4 o4 ON o4.OptionID = l.OptionField4
GO
I get an error that says "incorrect syntax near the keyword FROM
(FROM Listings l)
I upadted the view (added FROM) to the select statements as well
I prefer not to use t he function because I had to add an index to my openhours table on listingid and day in order to make it a little faster but if adding sql into view itself would be better that would be awesome

Answer 1

User defined function isn't usually the best performing solution. You could try just to add that SQL into the view / query by doing something like this (sorry, can't test this, hopefully there's no syntax errors):
select
L.ListingID,
isnull(H1.Hours, H2.Hours) as Hours
from Listing L
outer apply (
select Hours OpenHours H WHERE H.Day = 7
AND H.ListingID = L.ListingID
) H1
outer apply (
select Hours OpenHours H WHERE Day = DATEPART(DW, GETDATE()) - 1
AND H.ListingID = L.ListingID
) H2