SQL Loop, If/Else, Case Statements

I have an SQL query that I am trying to edit to make it more effective.  I didn't write the original and I'm reasonably new to SQL so its kinda touch and go if I can figure something out.  The query basically pulls and displays some information from the database based on start and end dates and a index number (Called an LCCN in this case).  How it was originally written required the person executing it to go in and change dates and numbers in multiple places throughout the query, and it had to be run for times to cover each of the four LCCNs.

I'm trying to make it so there are very few changes that need to be done and they are all in the first few lines.  Also I'm trying to make it run all four LCCNs in one query.  The original is below.


SELECT
      YEAR(UpdateDate) as 'Year',
      DATENAME(mm,UpdateDate) as 'Month',
      SUM(LaborQuantity) as 'Total',
      COUNT(DISTINCT JobN) as 'Number of Jobs'
FROM
      JobLabor
WHERE
      UpdateDate BETWEEN (d '2006-01-01) AND (d '2006-03-01')

      -- Change the below based on press
        -- 52015              6/c Press
        -- 55215              PM
        -- 39010              M700
        -- 39100              DE
      AND LCCN = 52015

      -- Change the below to 0 for regular counts; 2 for rework; comment out for total count
      AND prefix = 0
      
GROUP BY
      YEAR(UpdateDate),
      MONTH(UpdateDate),
      DATENAME(mm,UpdateDate)
ORDER BY
      YEAR(UpdateDate),
      MONTH(UpdateDate),
      DATENAME(mm,UpdateDate)


This is what I have gotten so far with my changes.

DECLARE @StartDate DATETIME, @EndDate DATETIME, @CountType INT, @6C INT, @PM INT, @M700 INT, @DE INT
SET @StartDate = '2010-07-01'
SET @EndDate = '2010-08-31'
SET @CountType = 0
SET @6C = 52015
SET @PM = 55215
SET @M700 = 39010
SET @DE = 39100
SELECT
      YEAR(UpdateDate) as 'Year',
      DATENAME(mm,UpdateDate) as 'Month',
      SUM(LaborQuantity) as 'Total',
      COUNT(DISTINCT JobN) as 'Number of Jobs'
FROM
      JobLabor
WHERE
      UpdateDate BETWEEN @StartDate AND @EndDate

      -- Change the below based on press
        -- 52015              6/c Press
        -- 55215              PM
        -- 39010              M700
        -- 39100              DE
      AND LCCN = 52015

      -- Change the below to 0 for regular counts; 2 for rework; comment out for total count
      AND prefix = @CountType
GROUP BY
      YEAR(UpdateDate),
      MONTH(UpdateDate),
      DATENAME(mm,UpdateDate)
ORDER BY
      YEAR(UpdateDate),
      MONTH(UpdateDate),
      DATENAME(mm,UpdateDate)

So I can copy and paste everything from SELECT down four times and change the LCCN numbers to each of the four options, but I know that not only is that the wrong way of doing things, but its messy and if someone else is looking at the code they might not be able to figure it out.

So the main think I'm looking for is how to do a loop for the four LCCN numbers (I think it would have to start above SELECT, not quite sure how far down it would have to go).  I know the basics of loops in some other languages but I haven't been able to figure out exactly what I want to do here.  I've also gotten hints that I want to use a CASE statement to do what I want, but I know very little about them.

The other thing I want to do that isn't as major is embed the line
                         AND prefix = @CountType
in an IF ELSE statement so if the number @CountType is 0 or 2 (don't ask me why its those two, the database is how it is) then it runs but if its any other number then the AND prefix statement is skipped entirely (so we don't have to manually go in and edit it out when we want a total count).

I know this might not be super clear or I might be asking two many things at once, I did what I could to make it easy to understand but I'm still new to this myself.  Any help would be greatly appreciated, thanks.