Good morning,
Would it be possible to know that whether "union" is quicker than "left
join" in a general sense?
Queries:
========================
(1) union
select a.*, b.value
from a
left join b
union
select a.*, c.value
from a
left join c
(2) left join
select distinct a.*,
case when ... then
b.value
else
c.value
from a
left join b
left join c
Will (1) be more efficient than (2) or vice versa? Or it really depends
on data
Thanks a lot!
Lu Ying