Oracle 中的表变量样式实体

Question

我一直在寻找一些在 Oracle 中类似于 SQL Server 中的表变量的东西。我发现有人在 SO 上问这样的问题，人们总是说“是的，Oracle 有这个”，但示例表明实体根本不像 SQL Server。有人可以告诉我如何在 Oracle 中执行以下简单的 TSQL 解决方案吗？

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

有些答案可能会告诉您，Oracle 有表变量，并且在一定程度上确实如此。但是，大多数答案会告诉您根本不应该在 Oracle 中执行此操作；根本没有必要。

在你的情况下，我会简单地使用 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：我长期以来一直试图得到的答案在 Ben 的评论中，我将其包括在这里： “没有变量，您可以即时创建并加入标准 SQL @wcm 中的其他表，是的。可以创建许多不同类型的对象来允许您执行此操作，但不完全是就像在 T-SQL 中一样”。

Answer 2

如果我理解正确，那么如果我需要临时存储仅限于我的会话可见的数据，那么我将使用全局临时表。可能比存储在内存中的开销更大，但也有很多优点 - 收集关于它们的统计信息、索引它们，以及在不考虑内存消耗的情况下存储数据的能力。