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All the Perl that's Practical to Extract and Report

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  • Ignoring NULLs in COUNT (just as Abigail explained) is just consistent with other aggregate functions in SQL. For example, SUM(foo) sums up every column 'foo' except the null ones. So there's no magical transformation of null to 0 and no concern with exceptions raised because there are some nulls out there. Obviously this behavior is equivalent to converting NULLs to 0, but it is not so everywhere. MAX(foo) and MIN(foo) also work this way: ignore NULLs - which is good because they don't compare just numbers and converting NULLs to 0 could also distort the maxima and minima unexpectedly.

    To count rows, you may use COUNT(1) as well.