null值与任意值比较时都为fasle
not in 、"!="、"not like"条件过滤都会过滤掉null值的数据
SELECT * from temp;
SELECT * from temp where score not in (70);
返回null解决方法:
SELECT * from temp where score not in (70) or score is null;
SELECT * from temp where score IFNULL(score,'') != 70;