MySQL教程之技巧

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

 

错误！未找到目录项。
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
案例：
有如下表，要求就裱中所有沒有及格的成績，在每次增長0.1的基礎上，使他們剛好及格:

 

    Name     score

 

    Zhangshan   80

 

    Lishi       59

 

    Wangwu      50

 

    Songquan    69

 

while((select min(score) from tb_table)<60)

 

begin

 

update tb_table set score =score*1.01

 

where score<60

 

if  (select min(score) from tb_table)>60

 

  break

 

 else

 

    continue

 

end

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