比较表变量和临时表

1、回滚事务对表变量无效，回滚事务对临时表有效

SET NOCOUNT ON;

DECLARE @TestTable TABLE (
  RowID   INT IDENTITY PRIMARY KEY CLUSTERED,
  Name     VARCHAR(9) NOT NULL UNIQUE,
  Age     TINYINT NULL,
  rowguid UNIQUEIDENTIFIER NOT NULL DEFAULT(newid()));

begin tran

INSERT INTO @TestTable (Name, Age) VALUES ('Roy', 25),('中国风', 21);
rollback tran

SELECT 'Insert rows' as Action, * FROM @TestTable;
/*
Action	RowID	Name	Age	rowguid
Insert rows	1	Roy	25	84C4F6CC-3AB3-4D7D-8779-0DCF3414AB61
Insert rows	2	中国风	21	1DB02A77-F20E-4326-A4E4-023CE9F5DEA7
*/
go
if OBJECT_ID('Tempdb..#TestTable') is not null
	drop table #TestTable
CREATE TABLE #TestTable (
  RowID   INT IDENTITY PRIMARY KEY CLUSTERED,
  Name     VARCHAR(9) NOT NULL UNIQUE,
  Age     TINYINT NULL,
  rowguid UNIQUEIDENTIFIER NOT NULL DEFAULT(newid()));
 
 begin tran
 
INSERT INTO #TestTable (Name,Age) VALUES ('Roy', 25),('中国风', 21);
rollback tran
SELECT 'Insert rows' as Action,* FROM #TestTable
/*
无记录
*/

2、临时表支持用into生成临时表/TRUNCATE清空表/set identity_insert/drop table,表变量不支持

use tempdb
go
if OBJECT_ID('Tempdb..#TestTable') is not null
	drop table #TestTable
--into
select 1 as ID into #TestTable

--TRUNCATE
TRUNCATE table #TestTable
go
if OBJECT_ID('Tempdb..#TestTable2') is not null
	drop table #TestTable2
Create table #TestTable2(ID int identity,Num int)
go
set identity_insert #TestTable2 on;
insert into #TestTable2(ID,Num) values(1,20)
set identity_insert #TestTable2 off;
go
drop table #TestTable,#TestTable2

3、表变量可以在创建表时定义主健PRIMARY KEY和唯一约束UNIQUE和检查check

use tempdb
go
SET NOCOUNT ON;
-- 记录当前tempdb里的表对象ID
if OBJECT_ID('Tempdb..#test') is not null
	drop table #test
SELECT object_id 
  INTO #test 
  FROM tempdb.sys.tables;
GO

--创建表变量
DECLARE @temp TABLE (
    RowID INT NOT NULL,
    ColA INT NOT NULL check(ColA<10),
    ColB char(1),
    ColC char(1),
    ColD char(1),
    PRIMARY KEY NONCLUSTERED (RowID, ColA),
    UNIQUE CLUSTERED (ColB, ColC),
    UNIQUE NONCLUSTERED (ColC, ColD));

INSERT INTO @temp VALUES (1, 1, 'B', NULL, 'D');


--获取表变量对象的ID
DECLARE @object_id INT;
SELECT @object_id = 
  (SELECT object_id 
     FROM tempdb.sys.tables
   EXCEPT
   SELECT object_id 
     FROM #test);

-- 获取表变量的索引名

;with IXC
as
(
SELECT 	IXC.object_id,
		IXC.index_id,
		IXC.index_column_id,
		IXC.is_descending_key,
		IXC.is_included_column,
		column_name = C.name
  FROM tempdb.sys.index_columns IXC
       JOIN tempdb.sys.columns C
         ON IXC.object_id = C.object_id
        AND IXC.column_id = C.column_id
 WHERE IXC.object_id = @object_id
)
select 
		IX.object_id,
		index_name = IX.name,
		index_type_desc = IX.type_desc,
		IX.is_unique,
		IX.is_primary_key,
		IX.is_unique_constraint,
		IX.is_disabled,
		index_columns = STUFF(IXC_COL.index_columns, 1, 2, N'')
from tempdb.sys.indexes as IX
CROSS APPLY(
SELECT index_columns = 
(SELECT 
	N', ' + QUOTENAME(column_name)+ CASE is_descending_key WHEN 1 THEN N' DESC' ELSE N'' END
FROM IXC
WHERE object_id = IX.object_id AND index_id = IX.index_id AND is_included_column = 0 ORDER BY index_column_id FOR XML PATH(''), ROOT('r'), TYPE).value('/r[1]', 'nvarchar(max)')	
)IXC_COL
where IX.object_id= @object_id
/*
object_id	index_name	index_type_desc	is_unique	is_primary_key	is_unique_constraint	is_disabled	index_columns
1572200651	UQ__#5DB5E0C__D87C70A35F9E293D	CLUSTERED	1	0	1	0	[ColB], [ColC]
1572200651	UQ__#5DB5E0C__287C70A3627A95E8	NONCLUSTERED	1	0	1	0	[ColC], [ColD]
1572200651	PK__#5DB5E0C__A5CBEAB465570293	NONCLUSTERED	1	1	0	0	[RowID], [ColA]
*/
GO
drop table #test

4、临时表名116个字符，表变量支持128个字符

CREATE TABLE #TestTable12345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890 (
--                    ^         ^         ^         ^         ^         ^         ^         ^         ^         ^         ^         ^
--                   10         20        30        40        50        60        70        80        90       100       110       120
  RowID INT IDENTITY PRIMARY KEY CLUSTERED,
);
GO
/*
消息 193，级别 15，状态 1，第 2 行
以 '#TestTable12345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890' 开头的对象名或列名太长。最大长度为 116 个字符。
*/


declare      @TestTable1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678 TABLE(
--                    ^         ^         ^         ^         ^         ^         ^         ^         ^         ^         ^         ^
--                   10         20        30        40        50        60        70        80        90       100       110       120
  RowID INT IDENTITY PRIMARY KEY CLUSTERED);

5、查看表变量的日志变化

CHECKPOINT将当前数据库的全部脏页写入磁盘。“脏页”是已输入缓存区高速缓存且已修改但尚未写入磁盘的数据页。

USE tempdb 
GO
---- 截断日志，测试开始1
CHECKPOINT 
-- 记录当前tempdb里的表对象ID  
if OBJECT_ID('Tempdb..#test') is not null  
    drop table #test  
SELECT object_id   
  INTO #test   
  FROM tempdb.sys.tables;
go
DECLARE @TransactionTest TABLE (
ID INT PRIMARY KEY,
SomeCol VARCHAR(20)
);
--获取表变量对象的ID
DECLARE @object_id INT;  
SELECT @object_id =   
  (SELECT object_id   
     FROM tempdb.sys.tables  
   EXCEPT  
   SELECT object_id   
     FROM #test); 
     
INSERT INTO @TransactionTest (ID, SomeCol) VALUES (0,'Row1');
INSERT INTO @TransactionTest (ID, SomeCol) VALUES (1,'Row2');

BEGIN TRANSACTION;
INSERT INTO @TransactionTest (ID, SomeCol) VALUES (2,'Row3');
ROLLBACK TRANSACTION;

SELECT * FROM @TransactionTest;

SELECT Operation, AllocUnitName, [Begin Time], [End Time]
FROM fn_dblog(NULL, NULL)
where AllocUnitName like '%'+object_Name(@object_id)+'%'
GO

最后三条记录都是插入记录日志

USE tempdb 
GO
-- 截断日志，测试开始2
CHECKPOINT 
-- 记录当前tempdb里的表对象ID  
if OBJECT_ID('Tempdb..#test') is not null  
    drop table #test  
SELECT object_id   
  INTO #test   
  FROM tempdb.sys.tables;
go

DECLARE @TransactionTest TABLE (
ID INT PRIMARY KEY,
SomeCol VARCHAR(20)
);
--获取表变量对象的ID
DECLARE @object_id INT;  
SELECT @object_id =   
  (SELECT object_id   
     FROM tempdb.sys.tables  
   EXCEPT  
   SELECT object_id   
     FROM #test); 
     
INSERT INTO @TransactionTest (ID, SomeCol)
VALUES
(0,'Row1'),
(1,'Row2'),
(1,'Row3');--主健重复
SELECT * FROM @TransactionTest;
SELECT Operation, AllocUnitName, [Begin Time], [End Time] 
  FROM fn_dblog(NULL, NULL)
  where AllocUnitName like '%'+object_Name(@object_id)+'%';

插入第3条记录出错，有删除前两条的动作

 

6、临时表有两种类型：本地表和全局表。它们在名称、可见性以及可用性上有区别。本地临时表的名称以单个数字符号 (#) 打头；它们仅对当前的用户连接是可见的；当用户从 SQL Server 实例断开连接时被删除。全局临时表的名称以两个数字符号 (##) 打头，创建后对任何用户都是可见的，当所有引用该表的用户从 SQL Server 断开连接时被删除。

--本地临时表
if OBJECT_ID('Tempdb..#1') is not null
	drop table #1
exec('select 1 as ID into #1')
select * from #1
/*
(1 行受影响)
消息 208，级别 16，状态 0，第 4 行
对象名 '#1' 无效。
*/

--全局临时表
if OBJECT_ID('Tempdb..##1') is not null
	drop table #1
exec('select 1 as ID into ##1')
select * from ##1
/*
ID
1
*/