[英]Conditionally Select additional rows from another table
我有两个表:
TableA
PK Alpha Critter Etc
1 A zebra apple
2 C lion orange
3 R giraffe banana
4 D gopher pear
TableC
PK Alpha Animal Misc
1 D beaver kiwi
2 D camel avacado
我需要这个结果:
Result
PK Alpha Critter Etc
22 A zebra apple
23 C lion orange
24 R giraffe banana
25 D gopher pear
26 D beaver kiwi
27 D camel avacado
如果TableA.Alpha的值等于一个以上具有相同值的TableC.Alpha,则Select将为:
Select TA.Alpha, TA.Critter, TA.Etc
From TableA TA
和
Select TC.Alpha, TC.Animal, TC.Misc
From TableC TC
在单独的行上(在上面的示例中为3行)
否则就是
Select TA.Alpha, TA.Critter, TA.Etc
From TableA TA
(一行)
我可能会使用CTE。 就像是:
With T_CTE (Alpha,CountAlpha)
AS
(SELECT
TC. Alpha, COUNT(TC.Alpha) as CountAlpha
FROM TableC TC
GROUP BY TC.Alpha
HAVING (COUNT(TC.Alpha) > 1 ))
Select TA.Alpha, TA.Critter, TA.Etc
From TableA TA
case when T_CTE.Alpha is not null then...else...end
left join T_CTE on T_CTE.Alpha = TA.Alpha
TableA.Alpha是唯一的。 TableC.Alpha不是唯一的。
我可以为其他行调用另一个选择吗? 有没有更好的方法? 我还考虑过创建临时表并从中选择。 这是一个较大查询的一部分,但是我现在要专注于这一部分。 有什么建议么? 谢谢。
就像是
;with cte as (
select A.Alpha, count(*) as cnt
from TableA as A
inner join TableC as C on C.Alpha = A.Alpha
group by A.Alpha
having count(*) > 1
)
select A.Alpha, A.Critter, A.Etc
from TableA as A
union all
select C.Alpha, C.Animal, C.Misc
from TableC as C
where C.Alpha in (select T.Alpha from cte as T)
sql小提琴演示 -我在TableC中添加了一行以检查是否包含它
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