The sql can be predigest to:
select random() from a where random()<0.5;
\d a
Table "public.a"
Column | Type | Modifiers
--------+---------+-----------
a | integer |
This query can get about a half rows in the table 'a'.
When search a row, postgresql calcuate random() twice.
_________________________________________________________
Do You Yahoo!?
登記免費的 @yahoo.com 中文電子郵件 @ http://chinese.mail.yahoo.com
Get your free @yahoo.com address at http://chinese.mail.yahoo.com