Oracle里表连接支持标准写法,但也有Oracle特殊的写法,这两种写法在某些场景下会有差异,推荐使用标准写法,这里只是介绍表连接标准语法及了解Oracle的特殊写法。
标准连接语法:
select table1.column , table2.column
from table1
[corss join table2]
[national jon table2]
[join table2 using (column)]
[join table2 on (table1.column=table2.column)]
[left | right | full outer join table2 on (table1.column=table2.column)];
实际使用中on关键字后的连接字段不用括号也可以正常使用。
多表连接:
--先连接table4和table5并将其结果集命名为table2,再与table1连接
select table1.column,table2.column
from table1
inner join
( select table4.column,table5.column
from table4 inner join table5
on table4.column =table5.column ) as table2
on table1.column=table2.column;
等同于
select table1.column ,table2.column
from table1 ,(select table4.column,table5.column
from table4,table5
where table4.column=table5.column) as table2
where table1.column=table2.column;
--连接table1,table2,table3,没有连接顺序之分
select table1.column,table2.column,table3.column
from table1 inner join table2
on table1.column=table2.column
inner join table3
on table1.column=table3.column;
等同于
select table1.column,table2.column,table3.column
from table1,table2.table3
where table1.column=table2.column and table1.column=table3.column;
内连接:
标准写法:
select table.column , table2.column
from table1 inner join table2 on (table1.column=table2.column);
Oracle 特殊写法:
select table.column , table2.column
from table1 ,table2
where table1.column=table2.column;
左连接:
标准写法:
select table.column , table2.column
from table1 left join table2 on (table1.column=table2.column);
Oracle 特殊写法:
select table.column , table2.column
from table1 ,table2
where table1.column=table2.column(+);
右连接:
标准写法:
select table.column , table2.column
from table1 right join table2 on (table1.column=table2.column);
Oracle 特殊写法:
select table.column , table2.column
from table1 ,table2
where table1.column(+)=table2.column;
全连接:
标准写法:
select table.column , table2.column
from table1 full join table2 on (table1.column=table2.column);
Oracle 特殊写法:
select table.column , table2.column
from table1 ,table2
where table1.column(+)=table2.column(+);