MySQL版本为5.6
大部分运算会忽略NULL行，个别有例外（如聚合、排序）。
具体见下表：
如果就是要统计NULL行，可以利用
if求和解决：sum(if(column is null, 1, 0))
样例如下：
mysql> create table test_count(v int);mysql> insert into test_count values (1), (2), (NULL);mysql> select * from test_count;+------+| v |+------+| 1 || 2 || NULL |+------+select count(*), count(1), count(v), sum(if(v is null, 1, 0)) countOfNull, sum(v), avg(v), min(v), max(v) from test_count;+----------+----------+----------+-------------+--------+--------+--------+--------+| count(*) | count(1) | count(v) | countOfNull | sum(v) | avg(v) | min(v) | max(v) |+----------+----------+----------+-------------+--------+--------+--------+--------+| 3 | 3 | 2 | 1 |3 | 1.5000 |1 |2 |+----------+----------+----------+-------------+--------+--------+--------+--------+
MySQL官方文档1 ：/doc/refman/5.6/en/problems-with-null.html ↩︎
MySQL官方文档2 ：/doc/refman/5.6/en/working-with-null.html ↩︎
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