SQL while循环

ALTER Proc [dbo].[p_GetServerDataCursor]
AS
BEGIN
   IF EXISTS ( SELECT  * FROM    sys.objects WHERE   object_id = OBJECT_ID(N'[dbo].[#ttableName]') AND type IN ( N'U' ) )
            BEGIN
                DROP TABLE [dbo].[#ttableName]
            END
    IF EXISTS ( SELECT  *
                    FROM    sys.objects
                    WHERE   object_id = OBJECT_ID(N'[dbo].[#tmpReturnData]')
                            AND type IN ( N'U' ) )
            BEGIN
                DROP TABLE [dbo].[#tmpReturnData]
            END
declare @orderNum varchar(255)
--创建临时表存储tagId
create table #ttableName(id int identity(1,1),Orders varchar(255))
--创建临时表返回数据
create table #tmpReturnData(id int identity(1,1),openid varchar(100),tagid varchar(100))
--定义循环变量，行数，总数
declare @n int,@rows int,@count varchar(1000),@a varchar(100)
--查询去重复tagId插入ttableName中
insert #ttableName(orders) select distinct tagId from Log_TagIdRecord where openId !='null' and IsServer=0
--row获取tagid行数    rowcount 返回受上一语句影响的行数。如果行数大于20 亿，请使用ROWCOUNT_BIG。
select @rows =@@rowcount
set @n=1
while @n<=@rows
begin
     --@count查询数量根据，ttableName表ID自增长根据@n循环每行数据
    select @count=COUNT( distinct openId) from Log_TagIdRecord where tagId=(select Orders from #ttableName where id=@n) and openId !='null'and IsServer=0;
     select @a=Orders from #ttableName where id=@n;
    IF(@count>49)
      BEGIN
        insert #tmpReturnData  select  distinct top 50 openId,tagId from Log_TagIdRecord where tagId=(select Orders from #ttableName where id=@n) and openId !='null'and IsServer=0;
     update  Log_TagIdRecord  set IsServer=1 where openId in (select openid from #tmpReturnData) and tagId in (select tagid from #tmpReturnData)
        break;
      END
     --@n增加
    select @n=@n+1
end
set @a='select * from #tmpReturnData'
EXEC (@a)
drop table #ttableName
drop table #tmpReturnData
END