Fastest SQL to get random rows from MySQL in LARGE and small databases

fastestRandomSelect.sql

# Ejemplo 1
SELECT * FROM post AS r1 JOIN (SELECT (RAND() * (SELECT MAX(postid) FROM post)) AS postid) AS r2 WHERE r1.postid >= r2.postid ORDER BY r1.postid ASC LIMIT 10

# Ejemplo 2
SELECT * FROM (SELECT * FROM `comprobantes` WHERE `ind-estado` = 'procesando' OR (`ind-estado` = 'rechazado' AND `respuesta-xml` IS NULL)) AS r1 JOIN (SELECT (RAND() * (SELECT MAX(id) FROM comprobantes)) AS id) AS r2 WHERE r1.id >= r2.id ORDER BY r1.id ASC LIMIT 100