Sql的基礎知識技巧（三）

三、技巧
1、1=1，1=2 的使用，在 SQL 語句組合時用的較多
“where 1=1” 是表示選擇全部
“where 1=2”全部不選，
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

我們可以直接寫成
錯誤！未找到目錄項。
set @strSQL = 'select count(*) as Total from [' + @tblName + ']
where 1=1 '+ @strWhere

2、收縮資料庫
--重建索引 DBCC REINDEX DBCC INDEXDEFRAG
--收縮數據和日誌 DBCC SHRINKDB DBCC SHRINKFILE

3、壓縮資料庫 dbcc shrinkdatabase(dbname)

4、轉移資料庫給新用戶以已存在用戶許可權
exec sp_change_users_login 'update_one','newname','oldname' go

5、檢查備份集 RESTORE VERIFYONLY from disk='E:\dvbbs.bak'

6、修複資料庫
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、日誌清除
SET NOCOUNT ON
DECLARE @LogicalFileName sysname,
@MaxMinutes INT,
@NewSize INT

USE tablename -- 要操作的資料庫名
SELECT @LogicalFileName = 'tablename_log', -- 日誌文件名
@MaxMinutes = 10, -- Limit on time allowed to wrap log.
@NewSize = 1 -- 你想設定的日誌文件的大小(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 = @Logical FileName)
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
ELECT '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、說明：更改某個表
exec sp_changeobjectowner 'tablename','dbo'

9、存儲更改全部表
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 中直接迴圈寫入數據
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