??????????????????????????????

???????????? ???????[ 2016/1/19 10:38:43 ] ????????????? ???????

?????.??????
????1.left join
?????????SQL???select * from student left join course on student.ID=course.ID
???????????????left join????????У????????????????????????????ж?????????????????(NULL).
????2.?????? right join ?? right outer join
????SQL???select * from student right join course on student.ID=course.ID
???????????????right join????????У????????????????????????????ж???????????????(NULL)??
????3??????????? full join ?? full outer join
????SQL???select * from student full join course on student.ID=course.ID
????????????????full join?????????????е??У??????????????????????????????ж?????????????????(NULL)???????????????????????????????ж?????????????????(NULL)??
??????.??????
?????????? join ?? inner join
????SQL???select * from student inner join course on student.ID=course.ID
????????????select * from student??course where student.ID=course.ID
??????.????????
????1.??????? WHERE ???????????????????????漰?????????????????????????????????????????????????????????С??
????SQL???select * from student cross join course
?????????????????????SQL????WHERE??????????SQL:select * from student cross join course where student.ID=course.ID
?????????????????????????????????inner join?????н???????