DISTINCT over SUMMARIZE

[karun_r]

I have a measure that follows the pattern as mentioned below

Test Adds =
CALCULATE (
    SUMX (
        DISTINCT ( SUMMARIZE ( Sales, Sales[Order Date], Sales[Order Number] ) ),
        IF ( Sales[Sales Amount] > 0, 1, 0 )
    )
)

I was wondering if I really need the DISTINCT over a SUMMARIZE call as the latter would already return unique combinations of order date and order number. Also, is there a better way to calculate the total number of orders for each day for which the sales amount > 0 ?