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(+);