oracle ×óÁ¬½ÓÎÊÌâ

select a.id, b.id
  from a, b
where a.cn = b.cn(+)
  and b.type(+) = '1'


select a.id, b.id
  from a, b
where a.cn = b.cn(+)
  and b.type = '1'

Õâ2¶ÎsqlÎÄÖ´Ðнá¹ûÓÐʲô²»Ò»Ñù£¿

---

with a as(select 1 id,'a' str from dual
  union all select 2,'a' from dual
  union all select 3,'a' from dual),
b as(select 1 id,'b' str from dual
  union all select 2,null from dual)
select * from a,b
where a.id=b.id(+)
  and b.str='b'

b.strºóÃæÌíÉϺÍÈ¥µô(+)¿´¿´½á¹ûÓÐʲô²»Í¬

---

Â¥Ö÷µÄÕâÖÖд·¨²»ÊìϤ. ½¨ÒéÓÃleft join, ÕâÖÖд·¨ÔڿɶÁÐÔÉÏÒªºÃµã.  ÖÁÓÚ½á¹ûÓÐʲô²»Ò»Ñù£¬Â¥Ö÷ÔËÐÐһϾÍÖªµÀÁË

SELECT A.id, A.name from A LEFT JOIN B ON A.id=B.id where A.id=2

---

ÒýÓÃ

µÚÒ»¸öÏ൱ÓÚ
select a.id, b.id
  from a left join b
on a.cn = b.cn
  and b.type = '1'

µÚ¶þ¸öÏ൱ÓÚ
select a.id, b.id
  from a left join b
on a.cn = b.cn
where b.type = '1'

¶Ô£¬¿ÉÒÔ°´ÕÕ¿ñÀÇÕâÑùµÄ·½Ê½¸Ä³Éleft join

ÎÒºÍDaveÒ»Ñù£¬¸üϲ»¶ÓÃleft join£¬ÊìϤ¶øÇÒÊÇSQL±ê×¼

---

лл¸÷λÀ²£¡