Oracle analysis function over and MySQL achieve similar effects

（1） Analysis function ：

rank ( ) over ( [query_partition_clause]order_by_clause )

dense_rank ( ) over([query_partition_clause] order_by_clause )

rownumber ( )  over ([query_partition_clause]order_by_clause )

It can be sorted by the specified fields , Sort the result set of the same grouping field , among partition by For group fields ,order by Specify sort fields

over Not to be used alone , To sum up and analyze functions ：rank(),dense_rank(),row_number() And so on

（2）Oracle Analyze the difference between functions and aggregate functions ：

        Analytic functions are used to calculate some aggregate value based on groups , It differs from the aggregate function in that it returns multiple rows for each group , The aggregate function returns only one line for each group .

（3） The Works of Liezi

Ranking after grouping , example ：

         select* from

                   (

select a.*,row_number() over(PARTITION BY project_id order by task_Assign_time desc) asrId

                   fromrate_task_info a

                   )

                   where  rId=1

(4)MySQL Implementation examples

SELECT * from(

select @rownum:[email protected]+1 rownum,a.*,

   if(@objno=a.project_id or (@objno is null and a.project_id is null),

           @rank:[email protected]+1,

           @rank:=1) as row_number,

   @objno:=a.project_id

   from(SELECT * from rate_task_info where current_node=700 order by project_id,task_Assign_timedesc)a,

   (select @rownum :=0,@objno:=null,@rank:=0)b

)t

where t.row_number=1;