如何在 MS SQL 中连接多个列的不同值？

Question

我有一个table这样的

id	type 1	type 2	type 3	type 4	type 5
1	a	b	b	not available	not available
2	c	c	a	not available	not available
3	not available	not available	not available	not available	not available

什么查询将帮助我对这些列中的不同值进行连接，并摆脱“不可用”，即：

id	types
1	a, b
2	c, a
3

Answer 1

假设not available表示null，你可以这样做：

select
  x.id,
  group_concat(distinct t) as types
from (select id from t) x
left join (
  select id, type1 as t from t
  union all select id, type2 from t
  union all select id, type3 from t
  union all select id, type4 from t
  union all select id, type5 from t
) y on y.id = x.id
group by x.id
order by x.id

结果：

 id  types 
 --- ----- 
 1   a,b   
 2   a,c   
 3

参见 db<>fiddle 中的示例。

Answer 2

您可以使用 CROSS APPLY

select
  id,
  string_agg(s.tp, ',') as types
from t
cross apply (
  select type1 union 
  select type2 union
  select type3 union
  select type4 union
  select type5  
) s(tp)
group by id
order by id;

db<>fiddle

如何在 MS SQL 中连接多个列的不同值？

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