Difference between conditional expression outside/inside the aggregation function?

Mon, 08 Dec 2014 10:28:17 GMT

What is the difference between

A conditional expression outside the aggregation function, e.g. If( <Condition>, Sum( <Expression> ) )
A conditional expression inside the aggregation function, e.g. Sum( If( <Condition>, <Expression> ) )...

I got an article regarding this

but still couldn't be able to clear my confusion.. Please let me know about this..

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