return random 5 records from last 20 records

Simply I have the following

table wit开发者_StackOverflowh records , i want to return randomly 5 records from the last 20 record (order by id desc)

so how we can do it fast thanks for help.

select * from
(
  select * from your_table 
  order by id desc limit 20
) as lastest_results
order by rand()
limit 5;

Use an inner query to return the last 20, and an outer query to select 5 of them randomly. This may be slow though.

SELECT * FROM (SELECT * FROM table ORDER BY id DESC LIMIT 20) t ORDER BY RAND() LIMIT 5;  

This is a slow method but it gets the JOB done:

ORDER BY RAND()
LIMIT 5;

If you are using a large table this can become very slow, There are multiple alternative that you can read about here

Alternative to order by rand

You need something like

SELECT * FROM table ORDER BY RAND() LIMIT 5;

If you have a time parameter to sort them by for example the last 20 records then use this.

SELECT * FROM table ORDER BY insert_time DESC, RAND() LIMIT 5;

OR

SELECT * FROM table ORDER BY id DESC, RAND() LIMIT 5;