将Oracle两个列合并成一个列 SQL怎么写？
比如 有一张表n
字段
a b
1 4
2 5
3 6
合并后为
c
1
2
3
4
5
6
select A from n
union
select B from n
select concat(n.a,n.b) from n;
select a||b from n;
select a as c from n
union all
select b from n
oralce中一般用select a||b as c from table
select * from A
union all(不去重)
select * from B