4、基表。视图的修改视图中的SELECT语句不能直接修改方法:在创建视图的CREATE语句中使用ORREPLACE选项。带ORREPLACE选项的CREATE语句格式为:CREATE OR REPLACE VIEWview_nameASSELECTcolumn_name(s)FROMtable_nameWHEREcondition这样在创建视图时,如果视图不存在,则创建它。如果已经存在一个同名的视图,那么先删除这个视图,然后再根据SELECT语句创建新视图,用这个新视图代替原来的视图。Intersect和Min
5、usluxinfemale25tomfemale26mary1male27moneymale27tonymale28tony1male19luxinfemale25tomfemale26mary2male27moneymale27tonymale28tony2male19TABLEA:TABLEB:SELECT*FROMTABLEAINTERSECTSELECT*FROMTABLEB;结果:NAME SEX AGE------------------------------
6、luxinfemale25tomfemale26moneymale27tonymale28SELECT*FROMTABLEAMINUSSELECT*FROMTABLEB;结果:NAME SEX AGE------------------------------mary1 male 27tony1 male 19SELECT*FROMTABLEBMINUSSELECT*FROMTABLEA;结果
7、:NAME SEX AGE------------------------------mary2 male 27tony2 male 19UNION、UNIONALL、INTERSECT和MINUS总结Union,对两个结果集进行并集操作,不包括重复行;UnionAll,对两个结果集进行并集操作,包括重复行;Intersect,对两个结果集进行交集操作,不包括重复行;Minus,对两个结果集进行差操