如何？
select case when a.id is null then b.ID else a.id end as ID,
A.AName,A.BName,b.name CName
from
(
select case when a.id is null then b.ID else a.id end as ID,
a.Name AName,b.Name BName
from
(select 1 ID, 'A' as Name
union
select 2, 'B'
union
select 3, 'C'
union
select 4 ,'D') A
full join
(select 2 ID,'K' as Name
union
select 3,'E'
union
select 7,'F'
union
select 8,'G') B on(a.id=b.id) ) a
full join
(select 1 id,'I' name
union
select 4,'J'
union
select 9,'K'
union
select 3,'L') b on(a.id=b.id)
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