如何在sql server中使用where子句之后的case

这是我的数据。如果价格为空，我只想显示A类数据 然后显示B类价格。我试过了，但不知道我是怎么表现出来的 资料

运行此查询时，只显示A类数据

select * from tbl1
where category = case when price is null then 'B' else 'A' end

---

使用

左连接和
合并（）
（也可以使用
isnull（）
）：

coalesce（）
将按从左到右的顺序返回参数中的第一个非
null
值

rextester演示：

返回：

select a.Category, a.Item, coalesce(a.Price,b.Price) as Price
from yourtable a
  left join yourtable b
    on a.Item = b.Item
   and b.category = 'B'
where a.category = 'A'

参考：




类似这样的东西

+----------+-----------+-------+
| Category |   Item    | Price |
+----------+-----------+-------+
| A        | Pen       |    10 |
| A        | Pencil    |    10 |
| A        | Note Book |    40 |
| A        | Bottle    |    80 |
| A        | Ball      |    50 |
| A        | Bag       |  1000 |
+----------+-----------+-------+

`

输出

;WITH cte(category,Item,Price)
AS
(
 SELECT 'A','Pen'       ,NULL  UNION ALL
 SELECT 'B','Pen'       ,10    UNION ALL
 SELECT 'A','Pencil'    ,10    UNION ALL
 SELECT 'B','Pencil'    ,8     UNION ALL
 SELECT 'C','Pencil'    ,7     UNION ALL
 SELECT 'A','Note Book' ,40    UNION ALL
 SELECT 'B','Note Book' ,30    UNION ALL
 SELECT 'C','Note Book' ,20    UNION ALL
 SELECT 'A','Bottle'    ,NULL  UNION ALL
 SELECT 'B','Bottle'    ,80    UNION ALL
 SELECT 'A','Ball'      ,50    UNION ALL
 SELECT 'B','Ball'      ,40    UNION ALL
 SELECT 'A','Bag'       ,1000  UNION ALL
 SELECT 'B','Bag'       ,800
 )
 SELECT category,Item,Price From
 (
 SELECT *,ROW_NUMBER()Over(Partition by Price order by Price)seq From
 (
 SELECT o.*  FROM cte i 
 INNER JOIN cte o
 ON o.category=i.category
 WHERE o.category='A' AND o.Price!=i.Price
 )dt
) Final
where Final.seq=1

值“B”的输出

category    Item    Price
A         Pencil    10
A         Note Book 40
A         Ball      50
A         Bag       1000

我的理解是，如果某个类别中的某个项目的价格为空，那么它应该从另一个有价格的类别中选取该特定项目

输出应该是什么样的？这里的问题是，当考虑
B
行时，他们试图对
A
行进行“推理”。在考虑是否在结果中包含
B
行时，他们希望
price
列的值来自
A
行。这不能用一个简单的
WHERE
条件来完成。
SELECT price
FROM table
WHERE
   category = CASE 
             WHEN price is not null THEN 'A'
             ELSE 'B'
            END

;WITH cte(category,Item,Price)
AS
(
 SELECT 'A','Pen'       ,NULL  UNION ALL
 SELECT 'B','Pen'       ,10    UNION ALL
 SELECT 'A','Pencil'    ,10    UNION ALL
 SELECT 'B','Pencil'    ,8     UNION ALL
 SELECT 'C','Pencil'    ,7     UNION ALL
 SELECT 'A','Note Book' ,40    UNION ALL
 SELECT 'B','Note Book' ,30    UNION ALL
 SELECT 'C','Note Book' ,20    UNION ALL
 SELECT 'A','Bottle'    ,NULL  UNION ALL
 SELECT 'B','Bottle'    ,80    UNION ALL
 SELECT 'A','Ball'      ,50    UNION ALL
 SELECT 'B','Ball'      ,40    UNION ALL
 SELECT 'A','Bag'       ,1000  UNION ALL
 SELECT 'B','Bag'       ,800
 )
 SELECT category,Item,Price From
 (
 SELECT *,ROW_NUMBER()Over(Partition by Price order by Price)seq From
 (
 SELECT o.*  FROM cte i 
 INNER JOIN cte o
 ON o.category=i.category
 WHERE o.category='A' AND o.Price!=i.Price
 )dt
) Final
where Final.seq=1

category    Item    Price
A         Pencil    10
A         Note Book 40
A         Ball      50
A         Bag       1000

category    Item        Price
--------------------------------
B           Pencil      8
B           Pen         10
B           Note Book   30
B           Ball        40
B           Bottle      80
B           Bag         800

--Filter records having prices
with CTETable as
(
Select distinct category, item, price 
from tbl1
where price is not null
)
--distinct items
select * from
(select category, item, price, ROW_NUMBER() over (Partition by Item order by 
Category) as RowNo from CTETable)
as c
where c.RowNo=1