SQL查询（三）技巧

 

三、技巧

 

1、1=1，1=2的使用，在SQL语句组合时用的较多

 

“where 1=1” 是表示选择全部   “where 1=2”全部不选，

如：

if @strWhere !=''

begin

set @strSQL = 'select count(*) as Total from [' + @tblName + '] where ' + @strWhere

end

else

begin

set @strSQL = 'select count(*) as Total from [' + @tblName + ']'

end

 

我们可以直接写成

set @strSQL = 'select count(*) as Total from [' + @tblName + '] where 1=1 安定 '+ @strWhere

 

2、收缩数据库

--重建索引

DBCC REINDEX

DBCC INDEXDEFRAG

--收缩数据和日志

DBCC SHRINKDB

DBCC SHRINKFILE

 

3、压缩数据库

dbcc shrinkdatabase(dbname)

 

4、转移数据库给新用户以已存在用户权限

exec sp_change_users_login 'update_one','newname','oldname'

go

 

5、检查备份集

RESTORE VERIFYONLY from disk='E:/dvbbs.bak'

 

6、修复数据库

ALTER DATABASE [dvbbs] SET SINGLE_USER

GO

DBCC CHECKDB('dvbbs',repair_allow_data_loss) WITH TABLOCK

GO

ALTER DATABASE [dvbbs] SET MULTI_USER

GO

 

7、日志清除

SET NOCOUNT ON

DECLARE @LogicalFileName sysname,

    @MaxMinutes INT,

    @NewSize INT

 

 

USE   tablename         -- 要操作的数据库名

SELECT @LogicalFileName = 'tablename_log', -- 日志文件名

@MaxMinutes = 10,           -- Limit on time allowed to wrap log.

    @NewSize = 1             -- 你想设定的日志文件的大小(M)

 

-- Setup / initialize

DECLARE @OriginalSize int

SELECT @OriginalSize = size

FROM sysfiles

WHERE name = @LogicalFileName

SELECT 'Original Size of ' + db_name() + ' LOG is ' +

    CONVERT(VARCHAR(30),@OriginalSize) + ' 8K pages or ' +

    CONVERT(VARCHAR(30),(@OriginalSize*8/1024)) + 'MB'

FROM sysfiles

WHERE name = @LogicalFileName

CREATE TABLE DummyTrans

(DummyColumn char (8000) not null)

 

 

DECLARE @Counter   INT,

    @StartTime DATETIME,

    @TruncLog VARCHAR(255)

SELECT @StartTime = GETDATE(),

    @TruncLog = 'BACKUP LOG ' + db_name() + ' WITH TRUNCATE_ONLY'

 

DBCC SHRINKFILE (@LogicalFileName, @NewSize)

EXEC (@TruncLog)

-- Wrap the log if necessary.

WHILE   @MaxMinutes > DATEDIFF (mi, @StartTime, GETDATE()) -- time has not expired

    AND @OriginalSize = (SELECT size FROM sysfiles WHERE name = @LogicalFileName)

    AND (@OriginalSize * 8 /1024) > @NewSize

BEGIN -- Outer loop.

  SELECT @Counter = 0

  WHILE ((@Counter < @OriginalSize / 16) AND (@Counter < 50000))

    BEGIN -- update

    INSERT DummyTrans VALUES ('Fill Log')

    DELETE DummyTrans

    SELECT @Counter = @Counter + 1

    END  

  EXEC (@TruncLog)

END  

SELECT 'Final Size of ' + db_name() + ' LOG is ' +

    CONVERT(VARCHAR(30),size) + ' 8K pages or ' +

    CONVERT(VARCHAR(30),(size*8/1024)) + 'MB'

FROM sysfiles

WHERE name = @LogicalFileName

DROP TABLE DummyTrans

SET NOCOUNT OFF

 

8、说明：更改某个表

exec sp_changeobjectowner 'tablename','dbo'

 

9、存储更改全部表

 

CREATE PROCEDURE dbo.User_ChangeObjectOwnerBatch

@OldOwner as NVARCHAR(128),

@NewOwner as NVARCHAR(128)

AS

 

DECLARE @Name   as NVARCHAR(128)

DECLARE @Owner as NVARCHAR(128)

DECLARE @OwnerName as NVARCHAR(128)

 

DECLARE curObject CURSOR FOR

select 'Name'   = name,

'Owner'   = user_name(uid)

from sysobjects

where user_name(uid)=@OldOwner

order by name

 

OPEN curObject

FETCH NEXT FROM curObject INTO @Name, @Owner

WHILE(@@FETCH_STATUS=0)

BEGIN  

if @Owner=@OldOwner

begin

set @OwnerName = @OldOwner + '.' + rtrim(@Name)

exec sp_changeobjectowner @OwnerName, @NewOwner

end

-- select @name,@NewOwner,@OldOwner

 

FETCH NEXT FROM curObject INTO @Name, @Owner

END

 

close curObject

deallocate curObject

GO

 

 

10、SQL SERVER中直接循环写入数据

declare @i int

set @i=1

while @i<30

begin

  insert into test (userid) values(@i)

  set @i=@i+1

end

 

小记存储过程中经常用到的本周，本月，本年函数

Dateadd(wk,datediff(wk,0,getdate()),-1)

Dateadd(wk,datediff(wk,0,getdate()),6)

 

Dateadd(mm,datediff(mm,0,getdate()),0)

Dateadd(ms,-3,dateadd(mm,datediff(m,0,getdate())+1,0))

 

Dateadd(yy,datediff(yy,0,getdate()),0)

Dateadd(ms,-3,DATEADD(yy, DATEDIFF(yy,0,getdate())+1, 0))

 

上面的SQL代码只是一个时间段

Dateadd(wk,datediff(wk,0,getdate()),-1)

Dateadd(wk,datediff(wk,0,getdate()),6)

就是表示本周时间段.

下面的SQL的条件部分,就是查询时间段在本周范围内的:

Where Time BETWEEN Dateadd(wk,datediff(wk,0,getdate()),-1) AND Dateadd(wk,datediff(wk,0,getdate()),6)

而在存储过程中

select @begintime = Dateadd(wk,datediff(wk,0,getdate()),-1)

select @endtime = Dateadd(wk,datediff(wk,0,getdate()),6)