 This query displays price lists and the data used to perform
        price calculations. It avoids price calculations where possible.
        The UNION sets the sourcecode column to show how the price list entry
        was derived:  customer vs customer type vs customer type regex ..., etc.
        Then the outer query modifies the sourcecode to indicate
        item vs product category.
        TODO: possible improvements include removing OUTER JOINs with uom table
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