Temp table: A Temp table is easy to create and back up data. Table variable: But the table variable involves the effort when we usually create the normal tables. Temp table: Temp table result can be used by multiple users. Table variable: But the table variable can be used by the current user only.  Temp table: Temp table will be stored in the tempdb. It will make network traffic. When we have large data in the temp table then it has to work across the database. A Performance issue will exist. Table variable: But a table variable will store in the physical memory for some of the data, then later when the size increases it will be moved to the tempdb. Temp table: Temp table can do all the DDL operations. It allows creating the indexes, dropping, altering, etc.., Table variable: Whereas table variable won't allow doing the DDL operations. But the table variable allows us to create the clustered index only. Temp table: Temp table can be used for the current session or global. So that a multiple user session can utilize the results in the table. Table variable: But the table variable can be used up to that program. (Stored procedure) Temp table: Temp variable cannot use the transactions. When we do the DML operations with the temp table then it can be rollback or commit the transactions. Table variable: But we cannot do it for table variable. Temp table: Functions cannot use the temp variable. More over we cannot do the DML operation in the functions . Table variable: But the function allows us to use the table variable. But using the table variable we can do that. Temp table: The stored procedure will do the recompilation (can't use same execution plan) when we use the temp variable for every sub sequent calls. Table variable: Whereas the table variable won't do like that.

@wcm -实际上nit选择表变量不只是Ram -它可以部分存储在磁盘上。

临时表可以有索引，而表变量只能有主索引。如果速度是一个问题，表变量可以更快，但显然如果有很多记录，或者需要搜索聚集索引的临时表，那么临时表将更好。

好的背景文章

对于所有相信临时变量只存在于内存中的人

首先，表变量不一定存在于内存中。在内存压力下，属于表变量的页可以被推到tempdb。

在这里阅读文章:TempDB::表变量vs本地临时表

在SQL中，临时表存储在TempDB中，本地临时表只在当前会话中可见，在另一个会话中不可见。这可以在嵌套存储过程调用之间共享。全局临时表对所有其他会话可见，当最后一个连接引用表关闭时，它们将被销毁。例如,

Select Dept.DeptName, Dept.DeptId, COUNT(*) as TotalEmployees
into #TempEmpCount
from Tbl_EmpDetails Emp
join Tbl_Dept Dept
on Emp.DeptId = Dept.DeptId
group by DeptName, Dept.DeptId

表变量类似于tempTables，表变量也是在TempDB中创建的。表变量的作用域是声明表变量的批处理、存储过程或语句块。它们可以作为过程之间的参数传递。同样的查询可以使用Table变量by来编写

Declare @tblEmployeeCount table
(DeptName nvarchar(20),DeptId int, TotalEmployees int)
Insert @tblEmployeeCount
Select DeptName, Tbl_Dept.DeptId, COUNT(*) as TotalEmployees
from Tbl_EmpDetails
join Tbl_Dept
on Tbl_EmpDetails.DeptId = Tbl_Dept.DeptId
group by DeptName, Tbl_Dept.DeptId

在哪些情况下，一个会优于另一个?

对于较小的表(小于1000行)，使用临时变量，否则使用临时表。

Temp table: A Temp table is easy to create and back up data. Table variable: But the table variable involves the effort when we usually create the normal tables. Temp table: Temp table result can be used by multiple users. Table variable: But the table variable can be used by the current user only.  Temp table: Temp table will be stored in the tempdb. It will make network traffic. When we have large data in the temp table then it has to work across the database. A Performance issue will exist. Table variable: But a table variable will store in the physical memory for some of the data, then later when the size increases it will be moved to the tempdb. Temp table: Temp table can do all the DDL operations. It allows creating the indexes, dropping, altering, etc.., Table variable: Whereas table variable won't allow doing the DDL operations. But the table variable allows us to create the clustered index only. Temp table: Temp table can be used for the current session or global. So that a multiple user session can utilize the results in the table. Table variable: But the table variable can be used up to that program. (Stored procedure) Temp table: Temp variable cannot use the transactions. When we do the DML operations with the temp table then it can be rollback or commit the transactions. Table variable: But we cannot do it for table variable. Temp table: Functions cannot use the temp variable. More over we cannot do the DML operation in the functions . Table variable: But the function allows us to use the table variable. But using the table variable we can do that. Temp table: The stored procedure will do the recompilation (can't use same execution plan) when we use the temp variable for every sub sequent calls. Table variable: Whereas the table variable won't do like that.