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 tranINSERT INTO @TestTable (Name, Age) VALUES ('Roy', 25),('中国风', 21);rollback tranSELECT 'Insert rows' as Action, * FROM @TestTable;/*ActionRowIDNameAgerowguidInsert rows1Roy2584C4F6CC-3AB3-4D7D-8779-0DCF3414AB61Insert rows2中国风211DB02A77-F20E-4326-A4E4-023CE9F5DEA7*/goif OBJECT_ID('Tempdb..#TestTable') is not nulldrop table #TestTableCREATE 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 tranSELECT '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 tempdbgoif OBJECT_ID('Tempdb..#TestTable') is not nulldrop table #TestTable--intoselect 1 as ID into #TestTable--TRUNCATETRUNCATE table #TestTablegoif OBJECT_ID('Tempdb..#TestTable2') is not nulldrop table #TestTable2Create table #TestTable2(ID int identity,Num int)goset identity_insert #TestTable2 on;insert into #TestTable2(ID,Num) values(1,20)set identity_insert #TestTable2 off;godrop 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 tempdbgoSET NOCOUNT ON;-- 记录当前tempdb里的表对象IDif OBJECT_ID('Tempdb..#test') is not nulldrop table #testSELECT 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IDDECLARE @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 IXCas(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 IXCROSS APPLY(SELECT index_columns = (SELECT N', ' + QUOTENAME(column_name)+ CASE is_descending_key WHEN 1 THEN N' DESC' ELSE N'' ENDFROM IXCWHERE 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_COLwhere IX.object_id= @object_id/*object_idindex_nameindex_type_descis_uniqueis_primary_keyis_unique_constraintis_disabledindex_columns1572200651UQ__#5DB5E0C__D87C70A35F9E293DCLUSTERED1010[ColB], [ColC]1572200651UQ__#5DB5E0C__287C70A3627A95E8NONCLUSTERED1010[ColC], [ColD]1572200651PK__#5DB5E0C__A5CBEAB465570293NONCLUSTERED1100[RowID], [ColA]*/GOdrop 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1CHECKPOINT -- 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;goDECLARE @TransactionTest TABLE (ID INT PRIMARY KEY,SomeCol VARCHAR(20));--获取表变量对象的IDDECLARE @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2CHECKPOINT -- 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;goDECLARE @TransactionTest TABLE (ID INT PRIMARY KEY,SomeCol VARCHAR(20));--获取表变量对象的IDDECLARE @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 nulldrop table #1exec('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 nulldrop table #1exec('select 1 as ID into ##1')select * from ##1/*ID1*/