The problem with this approach is that it requires two scans of the base table.  Here is an approach that only requires one scan of the table.

[code...

It's really hard to say without something even remotely concrete to reference, but I think the first thing...

You didn't specify what start and end dates you used.  If you don't supply dates, then the parameters will default to NULL and no records will qualify.

You should...

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Check out the following articles:
Cross Tabs and Pivots, Part 1 – Converting Rows to Columns
Cross Tabs and Pivots, Part 2 - Dynamic Cross Tabs

Okay.  I did a quick test, and my intuition bore out:

Here are the results:
Method                         duration

Look at the following article which talks about using Windowed Functions to solve FIFO queues. FIFO Queues

Drew