Implementation of DB2 circular Query

DB2 circular query is a common problem. If we encounter a large table problem, how can we implement Circular query for large tables? The following describes how to implement the Circular query of DB2 in large tables for your reference.

Requirement Description:

There is a table with three fields, which are the departure time of the flight signal Logon Time.

Now we want to obtain the number of simultaneous users by day.

Our method is to divide the time into a time point every five minutes, and calculate the number of users who went online before the time point and went offline after the time point.

Then, it takes the most online users a day. The number of simultaneous online users for the day.

The implementation of DB2 cyclic query is as follows:

 
 

  
  
-- Original data table
  
  
Create table zhangmo_online (sid integer, logintime timestamp, logouttime timestamp );
  
  
 
  
  
-- Test Data
  
  
Insert into zhangmo_online
  
  
Select 51982112, current timestamp, current timestamp + 20 MINUTES from (values (1);
  
  
 
  
  
-- Create a sampling table for a five-minute period
  
  
Create table zhangmo_onlinenum (onlinetime varchar (20), onlinenum integer );
  
  
 
  
  
-- Create a sample pomelo Process
  
  
Create procedure zhangmo_onlinenum ()
  
  
Language SQL
  
  
Begin
  
  
Declare I timestamp;
  
  
Set I = TIMESTAMP ('2017-02-01 00:00:00 ');
  
  
While I 
  
  
Insert into zhangmo_onlinenum (onlinetime, onlinenum)
  
  
Select trim (char (year (I) |
  
  
Right ('00' | trim (char (month (I), 2) |
  
  
Right ('00' | trim (char (day (I), 2) |
  
  
Right ('00' | trim (char (hour (I), 2) |
  
  
Right ('00' | trim (char (minute (I), 2), count (distinct sid)
  
  
From zhangmo_online
  
  
Where logintime  I; 
  
  
Set ii = I + 5 MINUTES;
  
  
End while;
  
  
Commit;
  
  
End;
  
  
 
  
  
-- Execution Process
  
  
Call zhangmo_onlinenum ();
  
  
 
  
  
-- Get the final data
  
  
Select left (onlinetime, 10), max (onlinenum) from zhangmo_onlinenum
  
  
Group by left (onlinetime, 10 );
  
  
 
 
 

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