I found a good article which the author shows you how to select random records from table among different kind of databases.
Here are the example for SQLite, MySQL and PostgreSQL.
SELECT Field1, ..., Field2 FROM Table1 ORDER BY Random() LIMIT 1;
SELECT Field1, ..., FieldN FROM Table1 ORDER BY RAND() LIMIT 1;
SELECT "Field1", "...", "FieldN" FROM "Table1" ORDER BY RANDOM() LIMIT 1;
The number of return records depends on the LIMIT value and you could find other database SQL and the tests details at CarlJ.ca – Selecting Random Records With SQL.
PS: A reply in that article stated that there randomness could not scale well for large table. I don’t have any evidence to support this argument. But for my case, it is already enough. =P
Reference: CarlJ.ca – Selecting Random Records With SQL