Parameter error using DECLARE

i'm coming from an SSRS background. I'm mimicking a report we have in SSRS. i dont want to use a connector as we will be using the Power BI version from now on if we can get this working.

I've connected using a SQL statement and have a parameter called @Workspace and trying to add this dataset called @Location and this code below would do the work (this is a dataset i have on SSRS).

I tried using DECLARE but getting errors.

Any help appreciated 

IF @Workspace <> -1
BEGIN
SELECT
	Id, Name, WorkspaceId, SortGroup 
FROM 
	dbo.vw_pl_Locations
WHERE 
	Id = -1 OR
	(WorkspaceId = @Workspace AND
	Id <> @Workspace)
END

IF @Workspace = -1
BEGIN
SELECT
	Id, Name, WorkspaceId, SortGroup 
FROM 
	dbo.vw_pl_Locations
WHERE
	Id = -1 OR
	Id NOT IN (SELECT Id FROM dbo.vw_pl_Workspaces AS vpw)
END