一次优化小例子

 

        --accountRecord表主键是tradeno varchar(50)类型，没有其他合适的索引可用
        --数据量8000W，新建索引也不太现实
        --用此种方法，本来执行一次需要十秒左右，这种方法只需要一秒
        --第一次执行的时候取一次最小的tradeno，以后每次都会更新最小tradeno，大大提升性能！！！
        declare @i int =0
        declare @tradeno varchar(50)        
        while @i<10
        begin
            if @i=0
                select @tradeno=min(tradeno) from accountRecord where wCompleteTime  is null and CompleteTime is not null
            select @tradeno=min(tradeno) from accountRecord where tradeNo>=@tradeno and  wCompleteTime is null and CompleteTime is not null
            update  accountRecord set wCompleteTime =CompleteTime  where  1=1
            and tradeNo in (select top 20000 tradeNo from accountRecord  where tradeNo>=@tradeno and wCompleteTime  is null and CompleteTime is not null order by tradeNo asc)            
            set @i=@i+1
            PRINT CAST(@i AS VARCHAR(4))+'    '+@tradeno+'    '+convert(varchar(25),getdate(),121)+REPLICATE(' ',4000)
            WAITFOR DELAY '0:00:02'
        end