sql server 的游标

-- sql server 中的游标

--声明游标

/*

declare cursorname [insensitive] [scroll] cursor

for <select-查询块>

[for {read only|update[of<列名>[,...,n]]}]

Insensitive 表示把取出来的数据存入一个在tempdb库中创建的临时表，任何通过这个游标进行的操作，都会在这个临时表里进行。所有对基本表的改动都不会在用游标进行的操作中体现出来，不用该关键字，则用户对基本表所进行的任何操作都将在游标中得到体现。

Scroll: 指定所有的提取选项（first,last,prior,wext,relative,absolute)均可用，允许删除和更新（假定没有使用insensitive选项）

for read only :游标只读。不允许通过只读游标进行数据的更新。

for update[of <列名>[,...,n]]：游标是可修改的。定义在这个游标里可以更新的列。如果定义了[of<列名>[,...n]]，则只有其中的列可以被修改；否则，游标里的所有列都可以被修改。

*/

declare @tagname nvarchar(max)

declare @max_datetime datetime

declare mycursor cursor

for

select a.tagname,max(isnull(b.DateTime,0))

from tblfminfolive a

left join live_dblink.gb_scada_live.dbo.LiveData b on a.tagname=b.tagname and b.provider='TAX'

group by a.tagname;

-- 打开游标

open mycursor;

-- 提取数据

-- fetch[[next|prior|first|last|absoute n|relative n] from] <游标名> [into @变量名[,...,n]]

fetch next from mycursor into @tagname,@max_datetime;

/*全局变量@@fetch_status表示fetch语句的状态

0  表示提取正常

1 表示已经取到了数据集的末尾

其他值均表明操作出了问题

*/

-- 进入循环

while (@@fetch_status=0)

BEGIN

IF right(@tagname,2) !='YL'

-- 写入flux,PlusTotalFlux,ReverseTotalFlux  to 目标表

insert into live_dblink.gb_scada_live.dbo.LiveData(

provider,sitename,tagname,MeterName,DateTime,value)

select 'TAX',b.username,b.tagname,b.MeterName,a.readtime

,case right(@tagname,2)

when 'SL' then a.flux

when 'ZL' then a.plustotalflux

when 'FL' then a.reversetotalflux

end

FROM tblfmreaddata a ,tblfminfolive b

WHERE a.fmaddress+right(@tagname,3)=@tagname and b.tagname=@tagname

AND a.readtime>@max_datetime

ELSE

--写入 pressure  to 目标表

insert into live_dblink.gb_scada_live.dbo.LiveData(

provider,sitename,tagname,MeterName,DateTime,value)

select 'TAX',b.username,b.tagname,b.MeterName,a.readtime,isnull(a.pressure,0)

FROM tblfmreaddatapress a,tblfminfolive b

WHERE a.fmaddress+right(@tagname,3)=@tagname and b.tagname=@tagname

AND a.readtime>@max_datetime

-- 获取下一条数据

fetch next from mycusor into @tagname,@max_datetime;

END;

-- 关闭游标

close mycursor;

-- 释放游标

deallocate mycursor;

-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------

---  由于sql server 的未知原因，cursor未能成功执行，于是创建临时表，原理类似cursor,如下：

--------------------------------------------------------------------------------

declare @cun int

declare @maxcun int

declare @max_datetime datetime

declare @fmaddress varchar(40)

create table #tmp_fmaddress

(

pid int identity(1,1),

fmaddress varchar(100),

max_datetime datetime

)

insert into #tmp_fmaddress(fmaddress,max_datetime)

select a.fmaddress,max(isnull(b.DateTime,0))

from tblfminfolive a

left join live_dblink.gb_scada_live.dbo.LiveData b on a.tagname=b.tagname and b.provider='TAX'

and b.DateTime>dateadd(day,-2,getdate())

group by a.fmaddress

set @cun=1

select @maxcun=max(pid) from #tmp_fmaddress

-- 进入循环

while @cun<@maxcun+1

BEGIN

select @fmaddress=fmaddress,@max_datetime=max_datetime from #tmp_fmaddress where pid=@cun

------流量数据

select fmaddress,readtime,flux,PlusTotalFlux,ReverseTotalFlux

into #temp_flux

FROM tblfmreaddata WHERE fmaddress=@fmaddress

AND readtime>@max_datetime

AND readtime>dateadd(day,-2,getdate())

-----压力数据

select fmaddress,readtime, isnull(pressure,0) press

into #temp_press

FROM tblfmreaddatapress WHERE fmaddress=@fmaddress

AND readtime>@max_datetime

and readtime>dateadd(day,-2,getdate())

-- 写入flux,PlusTotalFlux,ReverseTotalFlux  to 目标表

insert into live_dblink.gb_scada_live.dbo.LiveData(

provider,sitename,tagname,MeterName,DateTime,value)

select 'TAX',b.username,b.tagname,b.MeterName,a.readtime

,case right(b.tagname,2)

when 'SL' then a.flux

when 'ZL' then a.plustotalflux

when 'FL' then a.reversetotalflux

end

FROM #temp_flux a,tblfminfolive b

where a.fmaddress=b.fmaddress and b.tagname!=@fmaddress+'_YL'

-- 写入 pressure

insert into live_dblink.gb_scada_live.dbo.LiveData(

provider,sitename,tagname,MeterName,DateTime,value)

select 'TAX',b.username,b.tagname,b.MeterName,a.readtime,a.press

FROM #temp_press a,tblfminfolive b

where a.fmaddress=b.fmaddress and b.tagname=@fmaddress+'_YL'

drop table #temp_flux

drop table #temp_press

-- 获取下一条数据

set @cun=@cun+1

END