选另一行

Question

我有一个看起来像这样的表：

ID   Type   Value
A    Z01    10
A    Z09    20
B    Z01    30
C    Z01    40
D    Z09    50
E    Z10    60

对于每个ID，我想检索一个值。 理想情况下，该值应来自Z01类型的行。 但是，如果Z01不可用，我会选择Z09。 如果没有可用的内容，我什么也不想选择。

结果将如下所示：

Id   Type   Value
A    Z01    10
B    Z01    30
C    Z01    40
D    Z09    50

如何使用T-SQL完成此操作？

Answer 1

这应该给您您想要的：

select *
from table t
where 1 = case 
              when t.type = 'Z01' 
                  then 1 
              when t.type = 'Z09' 
                    and not exists (select 1 from table where id = t.id and type = 'Z01')
                  then 1 
          else 0 
       end

使用更通用的方法的另一种方法是（重写CASE表达式）：

select *
from table
where type = 'Z01'
    OR (type = 'Z09' and not exists (select 1 from table where id = t.id and type = 'Z01'))

一个显而易见的可sargable方法（它将使您的查询使用表上适当的索引（如果存在））：

select *
from table
where type = `Z01`

union all
select *

from table
where type = `Z09`
    and not exists (select 1 from table where id = t.id and type = 'Z01')

当我说索引时，我指的是type列上的非聚集索引。

Answer 2

您可以使用这样的查询

;WITH cte
AS (SELECT
    *, ROW_NUMBER() OVER (PARTITION BY id ORDER BY type) AS rn
FROM yourtable
WHERE type IN ('Z01', 'Z09'))
SELECT
    id, type, value
FROM cte
WHERE rn = 1

Answer 3

我将使用窗口函数：

select t.*
from (select t.*,
             row_number() over (partition by id
                                order by (case when type = 'Z01' then 1
                                               when type = 'Z09' then 2
                                          end)
                               ) as seqnum
      from t
     ) t
where seqnum = 1;

我不完全理解“如果没有可用的东西，那么什么也不要选择”的说法。 如果您是说要“ Z01”，“ Z09”或什么都不想要，请执行以下操作：

select t.*
from (select t.*,
             row_number() over (partition by id order by type) as seqnum
      from t
      where type in ('Z01', 'Z09')
     ) t
where seqnum = 1;

where子句进行过滤，您可以按字母顺序对类型进行排序。

Answer 4

然后试试这个

 Select distinct a.id, 
    coalesce(t1.type, t9.type) type,
    case when t1.type is not null 
         then t1.value else t9.value end value
 From table a 
    left join table t1 
       on t1.id = a.id 
          and t1.type = 'Z01'
    left join table t9 
       on t9.id = a.id 
          and t9.type = 'Z09'
  Where a.type in ('Z01', 'Z09')  -- < -- this last to eliminate row E

Answer 5

像这样：

select distinct
base.Id,
Coalesce(z01.Type, any.Type) Type,
Coalesce(z01.Value, any.Value)
from (select distinct id from [table]) base
left outer join [table] z01
    on z01.id = base.id
    and z01.Type = 'Z01'
left outer join [table] any
    on any.id = base.id
    and any.type != 'Z01'

Answer 6

从WHERE子句开始。 仅选择带有Z01和Z09的条目。 然后使用ROW_NUMBER对您的行进行排名并保持最佳状态。

select id, type, value 
from
(
    select 
      id, type, value, 
      row_number() 
        over (partition by id order by case when type = 'Z01' then 1 else 2 end) as rn
    from mytable
    where type in ('Z01','Z09')
) ranked
where rn = 1;