oracle Èý±íÁ´½Ó²éѯÎÊÌâ

table a£»             
userid               
  1
  2
  3
  5

table b£»
userid
  1
  2
  3
  5

table c£»
userid
  2
  6
  7

½á¹ûΪ£º
userid
  1
  2
  3
  4
  5
  6
  7

sql¸ÃÈçºÎд£¿
SQL code:

select
a.userid as x
from a a,b b,c c
where a.userid= b.userid(+) and b.userid = c.userid(+)
²¢²»ÄÜ´ïµ½ÎÒÏëÒªµÄ½á¹û

---

Äãa,b,c ±íÖж¼ ûÓÐ4°¡

---

select id
from a
unial
select id
from b
unail
select id
from c

---

ÒýÓÃ

select id
from a
unial
select id
from b
unail
select id
from c

µ¥´ÊдÁË´íÁË£¬Ó¦¸ÃÊÇ union

---

--ÓÃunion
select id from t1
union
select id from t2
union
select id from t3
order by id

---

select a.userid userid from a
union
select b.userid userid from b
union
select c.userid u