Oracle中的表變量樣式實體

Question

我一直在尋找甲骨文的東西，它像SQL Server中的表變量一樣。我發現有人在這裏提出類似這樣的問題，而人們總是說「是的，Oracle有這樣的」，但是這些例子表明這些實體根本不像SQL Server。有人能告訴我如何在Oracle中執行以下簡單的TSQL解決方案嗎？

declare @users table (
    ID int, 
    Name varchar(50), 
    Age int, 
    Gender char(1) 
) 

;with users as (
    select 1001 as ID, 'Bob' as Name, 25 as Age, 'M' as Gender 
    union 
    select 1021 as ID, 'Sam' as Name, 29 as Age, 'F' 
) 
insert into @users (ID, Name, Age, Gender) 
select * from users 

declare @grades table (
    UserID int, 
    ClassID int, 
    Grade int 
) 

;with grades as (
    select 1001 as UserID , 120 as ClassID, 4 as Grade 
    Union 
    select 1001 as UserID , 220 as ClassID, 2 as Grade 
    Union 
    select 1021 as UserID , 130 as ClassID, 4 as Grade 
    Union 
    select 1021 as UserID , 230 as ClassID, 4 as Grade 
    Union 
    select 1021 as UserID , 340 as ClassID, 2 as Grade 
) 
insert into @grades 
select * from grades 

select u.ID, u.Name, GPA = AVG(cast(g.grade as decimal)) 
from @users u 
    inner join @grades g on u.ID=g.UserID 
group by u.ID, u.Name 

Answer 1

有些答案可能會告訴你Oracle有表變量，並且它在一定程度上確實存在。但是，大多數答案都會告訴你，你根本不應該在Oracle中這樣做;根本沒有必要。

在你的情況我會簡單地用一個CTE：

with users as (
    select 1001 as ID, 'Bob' as Name, 25 as Age, 'M' as Gender from dual 
    union 
    select 1021 as ID, 'Sam' as Name, 29 as Age, 'F' from dual 
     ) 
, grades as (
    select 1001 as UserID , 120 as ClassID, 4 as Grade from dual 
    Union 
    select 1001 as UserID , 220 as ClassID, 2 as Grade from dual 
    Union 
    select 1021 as UserID , 130 as ClassID, 4 as Grade from dual 
    Union 
    select 1021 as UserID , 230 as ClassID, 4 as Grade from dual 
    Union 
    select 1021 as UserID , 340 as ClassID, 2 as Grade from dual 
      ) 
select u.ID, u.Name, AVG(g.grade) as gpa 
    from users u 
    join grades g on u.ID = g.UserID 
group by u.ID, u.Name 

更新：我一直試圖讓很長一段時間是在Ben的評論答案下面，我包括在這裏： 「有沒有變量，你可以隨時創建並加入標準SQL @ wcm中的其他表格，是的。有許多不同類型的對象可以創建，可以讓你做到這一點，但不完全如你所願在T-SQL中「。

Answer 2

如果我理解正確，那麼如果我需要臨時存儲限於在會話中可見的數據，那麼我將使用全局臨時表。可能比在內存中存儲更多的開銷，但也有很多優勢 - 收集統計數據，對它們進行索引，以及存儲數據而不考慮內存消耗的能力。