Question

在SQL中，是否可以将WITH放在WITH？

中

以下面的查询为例，

WITH Temp ([Description], [Amount], [OverdueBy])
AS 
(select Description, SUM(Amount) as Amount, (DATEDIFF(day,DueDate,GETDATE())) as OverdueBy  from brvAPAllInvoices 
Where PaidDate is null and APCo = 1 and Amount > 0 
Group By Description, DueDate, APRef

)

select * from Temp

我想创建一个＆＃34;虚拟＆＃34;基于上述查询的临时表。是否可以使用另一个WITH来包含它？

有些事情如下：

WITH Temp2 ([Description], [Amount], [OverdueBy])
AS
(
WITH Temp ([Description], [Amount], [OverdueBy])
AS 
(select Description, SUM(Amount) as Amount, (DATEDIFF(day,DueDate,GETDATE())) as OverdueBy  from brvAPAllInvoices 
Where PaidDate is null and APCo = 1 and Amount > 0 
Group By Description, DueDate, APRef

)

select * from Temp)

select * from Temp2

Answer 1

不，您无法在CTE中定义CTE，但您可以在一个声明中定义多个CTE并引用其他CTE。

; with a as (
    select * from some_table
),
b as (
   select * 
   from another_table t
     inner join a ON (t.key = a.key)
)
select * 
from b

Answer 2

根据您的dbms，您可以拥有多个WITH语句，嵌套与否。（用PostgreSQL说明。）SQL Server doesn't allow nesting common table expressions。（搜索 CTE_query_definition 。）

<强>嵌套

with today as (
  with yesterday as (select current_date - interval '1' day as yesterday)
  select yesterday + interval '1' day as today from yesterday 
)
select cast(today as date) from today

today
--
2014-06-11

当您嵌套公用表表达式时，嵌套的CTE在其封闭的CTE之外是不可见的。

with today as (
  with yesterday as (select current_date - interval '1' day as yesterday)
  select yesterday + interval '1' day as today from yesterday 
)
select * from yesterday

ERROR: relation "yesterday" does not exist

<强>嵌套的

with yesterday as (
  select current_date - interval '1' day as yesterday
), 
today as (
  select yesterday + interval '1' day as today from yesterday 
)
select cast(yesterday as date) as dates from yesterday
union all
select cast(today as date) from today

dates
--
2014-06-10
2014-06-11

当您使用连续的，未经证实的CTE时，较早的CTE对后者可见，但反之亦然。

with today as (
  select yesterday + interval '1' day as today from yesterday 
),
yesterday as (
  select current_date - interval '1' day as yesterday
) 
select yesterday from yesterday
union all
select today from today

ERROR:  relation "yesterday" does not exist

Answer 3

您通常会执行以下操作;

WITH Temp ([Description], [Amount], [OverdueBy])
AS 
(select Description, SUM(Amount) as Amount, (DATEDIFF(day,DueDate,GETDATE())) as OverdueBy  from brvAPAllInvoices 
Where PaidDate is null and APCo = 1 and Amount > 0 
Group By Description, DueDate, APRef
), Temp2 ([Description], [Amount], [OverdueBy]) AS 
(
    SELECT * FROM Temp
)
select * from Temp2

在你做作的例子中，显然没有多大用处，因为两个表结构几乎相同。我倾向于将CTE视为命名派生表而不是临时表....即使它们不仅仅是派生表

在SQL中是否可以在WITH内使用WITH

3 个答案: