Paging SQL (rownum, row_number, deny_rank, rank)

Pseudo column ：rownum It is oracle Database built-in columns , Any table can use , It is used to display the row number of data in the table

rownum principle

（1） For base tables , stay insert Records are allocated in the order of insertion
（2） For subqueries , Display in the query order of the subquery

A simple example

---- Check out the lowest paid 5 Employee information select t.*,ROWNUM from (select emp.* from emp order by sal) twhere ROWNUM between 1 and 5;select t.*,ROWNUM from (select emp.* from emp order by sal) twhere ROWNUM in(1,2,3,4,5);select t.*,ROWNUM from (select emp.* from emp order by sal) twhere ROWNUM<=5;

The operation effect is as follows ：

notes ：

• rownum Can only be less than 、 Less than or equal to a certain number 、 be equal to 1、 Greater than or equal to 1、 be equal to 1

• rownum There are... For dynamic allocation 1 There are subsequent serial numbers , namely rownum Not greater than 1 namely 1 The number above and rownum Can not be equal to 1 The number above

Tuo

• row_number(): Need and over The windowing function is used in conjunction with , Sequence number of the sort and rownum Pseudo columns are the same , Serial number , Regardless of the equality of values （ Same value but different sequence number ）

• dense_rank(): It can be used to sort , Its serial number is continuous , Consider duplicate data , If the values are equal, the sequence number is the same

• rank(): It can be used to sort , Its serial number is discontinuous , Consider duplicate data , If the values are equal, the sequence numbers are the same

select e.*,row_number() over(order by sal desc) r from emp e;select e.*,dense_rank() over(order by sal desc) r from emp e;select e.*,rank() over(order by sal desc) r from emp e;select e.*,row_number()over(partition by deptno order by sal desc) r from emp e;

The operation effect is as follows ：

author ： Yun Wenwu

Game programming , A game development favorite ~

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