Aggregates are also a regular source of confusion with NULLs, both in how aggregates handle NULLs on input, and when aggregates return NULLs. Let’s look at the input case first:
CREATE TABLE aggtest (x INTEGER);
INSERT INTO aggtest VALUES (7), (8), (NULL);
SELECT COUNT(*), COUNT(x), SUM(x), MIN(x), MAX(x), AVG(x) FROM aggtest;
count | count | sum | min | max | avg
-------+-------+-----+-----+-----+--------------------
3 | 2 | 15 | 7 | 8 | 7.5000000000000000
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NULLs and Aggregates (Part 8/11)
