Oracle数据库关键字用法,MERGE、START WITH 、OVER(PARTITION BY) 、MINUS

1.MERGE 判断table1和table2是否满足ON中条件，如果满足则用table2表去更新table1表，如果不满足，则将table2表数据插入table1表但是有许多可选项,表关联更新

MERGE  INTO table1 a

    USING(

                 select b.id bid,b.name bname from table2 b left join table1 c on c.id = b.id

)bb on(a.id = bb.bid)

WHEN MATCHED THEN

UPDATE SET

        a.name = bb.bname

WHEN NOT MATCHED THEN

INSERT(

a.id,a.name

)VALUES(

bb.bid,bb.bname

);

2.START WITH… CONNECT BY PRIOR…的作用，简单来说，就是将一个树状结构存储在一张表里，列如菜单表

select * from table_menu start with menu_id= 210 connect by prior menu_id=menu_parent_id;

查询菜单id为210下所有子菜单包括id为210的菜单。

3.OVER(PARTITION BY)根据表中字段分割后在排序取第一条

select * from (select r.*, row_number() over(PARTITION BY 字段1，字段2 order by 字段3 desc) rn

from table1 r

) where rn = 1;

4.MINUS 表之间比较

select  id,name from table1

minus

select id,name from table2;

table1中有table2中无或者table1中id,name与table2中不同