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期中考试困难MySQL总结知识点ALL SOME(ANY)NULL带来的干扰 -> 将TF变成三值逻辑:有NULL值会影响ALL,如where gdp > all(select gdp from world where continent = 'Europe'),由于部分gdp为NULL,where gdp > NULL将不会成立。有NULL值会影响NOT IN,如WHER...