MySQL takes random data out of a table

Implemented randomly, the following statement was found from the manual to complete the task:

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

That's what Rand said in the handbook:

RAND ()

RAND (N)

Returns a random floating-point value in the range 0 through 1.0. If an integer parameter n is specified, it is used as a seed value.

Mysql> select RAND ();

-> 0.5925

Mysql> Select RAND (20);

-> 0.1811

Mysql> Select RAND (20);

-> 0.1811

Mysql> select RAND ();

-> 0.2079

Mysql> select RAND ();

-> 0.7888

You cannot use a column with the rand () value in an ORDER BY clause, because an order by will repeatedly compute the column multiple times. In MySQL3.23, however, you can do this: SELECT * FROM table_name ORDER BY RAND (), which is advantageous to getting a from select * from Table1,table2 WHERE a=b and C

Note that a rand () in a WHERE clause will be reassessed each time the where is executed.

But try it, 8,000 records of the table, the execution once needed 0.08 sec, a little slower. After consulting Google, get the following code:

SELECT *

From table_name as R1 JOIN

(SELECT ROUND (RAND () *

(SELECT MAX (ID)

From table_name)) as ID)

As R2

WHERE r1.id >= r2.id

ORDER BY R1.id ASC

LIMIT 5;

Execution efficiency requires 0.02 sec. Unfortunately, only MySQL 4.1.* above supports such subqueries.