Question

Is there a way to rewrite this SP, without a subquery. Basically the I.RemarkId can sometimes be null, i was trying to use a left join or left outer join. I want to return rows from flightinfo always and return the remark when the I.RemarkId is not null and just null in the remark column when I.remarkId is null.

ALTER PROCEDURE [dbo].[Peach_GetFlightInfoForRoute]
    @FlightDate datetime,   
    @Origin nvarchar(3),
    @dest nvarchar(3),
    @Lang nvarchar(2)
AS
SELECT 
     I.FlightNumber
    ,FlightDate
    ,STD
    ,(select [Message] FROM FlightRemarkDetail WHERE RemarkId = I.RemarkId WHERE LangCode = @Lang) As [Remark]
FROM 
     [FlightInfo] as [I]
JOIN
     [FlightNumbers] as [N]
ON  
    I.FlightNumber = N.FlightNumber 
WHERE 
    FlightDate = @FlightDate AND (@Origin='' OR @Origin = N.Origin) AND (@dest = '' OR @dest = N.Destination)

FlightInfo
===========
FlightNumber    nvarchar(16)
FlightDate  datetime    
STD nvarchar(4) 
RemarkId int NULL

FlightRemarkDetail
==================
RemarkDetailId  int 
RemarkId    int NOT NULL
LangCode    nvarchar(2) 
Message nvarchar(512)   

Answer 1

This LEFT OUTER JOIN would essentially be the same thing. LEFT OUTER JOIN makes it so it doesn’t require the child table to have a matching record. So if there isn’t a record in FlightRemarkDetail, it will simply show as a null (similar to the result you would get from your subquery). This is assuming that there is a 1 to 1 (or 1 to 0) match between FlightInfo and FlightRemarkDetail, though. If multiple FlightRemarkDetail records exist per FlightInfo, it will cause duplicate rows.

SELECT 
     I.FlightNumber
    ,FlightDate
    ,STD
    ,D.Message As [Remark]
FROM 
     [FlightInfo] as [I]
JOIN [FlightNumbers] as [N] ON I.FlightNumber = N.FlightNumber 
LEFT OUTER JOIN [FlightRemarkDetail] as [D] ON I.RemarkId = D.RemarkId
WHERE 
    FlightDate = @FlightDate AND (@Origin='' OR @Origin = N.Origin) AND (@dest = '' OR @dest = N.Destination)