How To: Mutiple Select Statements Where 2nd Uses Column Value For Each Record From The First

To clarify, I'm trying to create a hiearchial grid that will display projects and their sub projects.

The page the sproc is servicing is a search page where a user can display all projects by a customer or they can enter in a projectID and return info that way.  Thus you'll see If else in what I have listed below.  I highlighted in red the 2nd select statement I'm trying to get to run.  One problem is I'm getting an error:

Msg 156, Level 15, State 1, Procedure sp_GetProjects, Line 33

Incorrect syntax near the keyword 'ELSE'.

Think this has something to do with me trying to run 2 select statements in an IF.  Secondly, I'm not sure exactly what syntax I need to use to accomplish what I'm trying to do.  Again, the first select statement is creating a table with all projects that match the passed custID, the second select statement I'm trying to generate a 2nd table that will take the projectID for each row returned to the first table and find all rows with the same projectID's in the BillGroup table.

 I need these two tables returned to a dataset I'm populated with a sqldataadapter in .net so I can create a relationship between the two tables and then bind to a grid.

 

@custID nchar(25) = NULL,

@projectID bigint = NULL

IF @custID != 'null'

   SELECT p.projectID, p.Description FROM Projects p

    WHERE custID = @custID



     SELECT * FROM Projects p

     JOIN dbo.BillGroups bg ON p.projectID = bg.projectID



ELSE IF @projectID != -1

   SELECT projectID, Description FROM Projects



   WHERE projectID = @projectID

BEGIN

-- SET NOCOUNT ON added to prevent extra result sets from

-- interfering with SELECT statements.

SET NOCOUNT ON;

-- Insert statements for procedure here



END