While making joins in SQL you can have parameters which are passed in your query for getting result

ALTER PROC [dbo].[uspGetNudgesDetails]
@AccessToken VARCHAR(50),
@BeaconID VARCHAR(50)=NULL,
@CompanyID BIGINT =0,
@TargetUserID BIGINT=0 
AS



BEGIN


-- Get user and company

SELECT @TargetUserID=[ID] ,@CompanyID=[CompanyID]  from [User] WHERE AccessToken=@AccessToken

-- For general message with no location

SELECT N.[ID],N.[Message],N.[LocationID],N.[TargetUserID],N.[Url],CONCAT(U.[FirstName],U.[LastName]) AS [CreatedBy],CONVERT(VARCHAR(20), N.[CreatedDate], 103) as [CreatedDate],N.[DaysTillExpire],N.[HoursTillExpire] 
	FROM [NUDGE] AS N INNER JOIN  [User] AS U ON N.[CreatedBy]=U.[ID]
	WHERE N.[LocationID]=0 
	AND N.[TargetUserID]=@TargetUserID
	AND N.[IsDeleted]=0 
	AND N.[IsExpired]=0 
	AND N.[IsCompleted]=0 

	UNION

-- For location dependent messages

SELECT N.[ID],N.[Message],N.[LocationID],N.[TargetUserID],N.[Url],CONCAT(U.[FirstName],U.[LastName]) AS [CreatedBy],CONVERT(VARCHAR(20), N.[CreatedDate], 103) as [CreatedDate],N.[DaysTillExpire],N.[HoursTillExpire] 
	FROM [NUDGE] AS N INNER JOIN  [User] AS U ON N.[CreatedBy]=U.[ID]
	WHERE N.[LocationID]=(SELECT [LocationID] FROM [Location] WHERE [BeaconUUID]=@BeaconID and [CompanyID]=@CompanyID)
	AND N.[TargetUserID]=@TargetUserID
	AND N.[IsDeleted]=0 
	AND N.[IsExpired]=0 
	AND N.[IsCompleted]=0 

END

So what we do is we will create joins based on values passed to these parameters by passing default values if user does not provide any value while invoking it