mysql的基本语法及相应的练习,标对号的是没问题的,只有求交集和差集的时候执行不了,可能是mysql不支持intersect和minus ,背景黄色部分是进阶阶段-The basic syntax of mysql and the corresponding practice standard checkmark is no problem, only seeking the intersection and difference set when the execution can not, probably mysql does not support intersect, and minus the background in yellow is an advanced stage