sql 1st的结果:
select p1.t1, p2.t2, p2.t3 from
(select 'A' as t1,'' as t2,'' as t3 from dual ) p1 left join
(select '' as t1, '' as t2, '' as t3 from dual where 1=2) p2 on p1.t1 = p2.t1
是
A NULL NULL
sql第2的结果:
select p1.t1, p2.t2, p2.t3 from
(select 'B' as t1,'' as t2,'' as t3 from dual ) p1 left join
(select '' as t1, '' as t2, '' as t3 from dual where 1=2) p2 on …