MySQL:
SELECT column FROM table ORDER BY RAND() LIMIT 1
PostgreSQL:
SELECT column FROM table ORDER BY RANDOM() LIMIT 1
Microsoft SQL Server:
SELECT TOP 1 column FROM table ORDER BY NEWID()
IBM DB2:
SELECT column FROM table ORDER BY RAND() FETCH FIRST 1 ROWS ONLY
Oracle:
SELECT column FROM ( SELECT column FROM table ORDER BY dbms_random.value ) WHERE rownum = 1