php操作mysql 取 并集、交集、差集（对于同样结构的表）

并集

 mysqli_query($conn," truncate table usef "); 
 mysqli_query($conn,"INSERT INTO usef SELECT * FROM temptemp UNION SELECT * FROM tempff " );  

交集

 mysqli_query($conn," truncate table usef "); 
 mysqli_query($conn,"INSERT INTO usef select  tempff.* from tempff inner join temptemp on tempff.userid = temptemp.userid and tempff.riqi = temptemp.riqi "); 

差集

mysqli_query($conn," truncate table usef "); 
mysqli_query($conn,"INSERT INTO usef select distinct temptemp.* from tempff inner join temptemp on (tempff.userid = temptemp.userid and tempff.riqi = temptemp.riqi)");

注释：$conn 连接文件名
两个表名：temptemp 和 tempff
生成的表名：usef
以上三个表的结构都是一样的。
差集上比较麻烦，试了很多都不是我要的，最后这样的写法成功了，注意我的主键是两个哦，参考的亲们根据自己情况定，还有就是尽量不要用not in，效率很低，我用了内联的写法。