$seed= rand(); 

$result=mysql_query("select * from quotes  ORDER BY RAND($seed) LIMIT 1");

$num=mysql_numrows($result);

This case only 1 value will be returned.
(LIMIT 1). To get more results change the limit amount.

ADDDATE(date,INTERVAL expr type) 
ADDDATE(expr,days) 

When invoked with the INTERVAL form of the second argument, 
ADDDATE() is a synonym for DATE_ADD(). 

The related function SUBDATE() is a synonym for DATE_SUB(). 

mysql> SELECT DATE_ADD('2004-01-02', INTERVAL 31 DAY);
        -> '2004-02-02'

mysql> SELECT ADDDATE('2004-01-02', INTERVAL 31 DAY);
        -> '2004-02-02'

As of MySQL 4.1.1, the second syntax is allowed, where expr is a date or
 datetime expression and days is the number of days to be added to expr. 

mysql> SELECT ADDDATE('2004-01-02', 31);        
          -> '2004-02-02'


ADDTIME() was added in MySQL 4.1.1. 
CURDATE() 
Returns the current date as a value in 'YYYY-MM-DD' or YYYYMMDD 

format, depending on whether the function is used in a string or
 numeric context:
 
mysql> SELECT CURDATE();
        -> '2004-12-15'
mysql> SELECT CURDATE() + 0;
        -> 20041215

CURRENT_DATE 
CURRENT_DATE() 
CURRENT_DATE and CURRENT_DATE() are synonyms for CURDATE(). 
CURTIME() 
Returns the current time as a value in 'HH:MM:SS' or HHMMSS format, 

depending on whether the function is used in a string or numeric context: 

mysql> SELECT CURTIME();
        -> '23:50:26'

mysql> SELECT CURTIME() + 0;
        -> 235026

CURRENT_TIME 
CURRENT_TIME() 
CURRENT_TIME and CURRENT_TIME() are synonyms for CURTIME(). 
CURRENT_TIMESTAMP 
CURRENT_TIMESTAMP() 
CURRENT_TIMESTAMP and CURRENT_TIMESTAMP() are synonyms for NOW(). 

DATE(expr) 
Extracts the date part of the date or datetime expression expr. 

mysql> SELECT DATE('2003-12-31 01:02:03');
        -> '2003-12-31'

DATE() is available as of MySQL 4.1.1. 
DATEDIFF(expr,expr2) 
DATEDIFF() returns the number of days between the start date expr and the end 

 date expr2. expr and expr2 are date or date-and-time expressions. Only the 

 date parts of the values are used in the calculation. 

mysql> SELECT DATEDIFF('2004-01-02 23:59:59','2004-01-01');
        -> 1

mysql> SELECT DATEDIFF('2004-01-31 23:59:59','2004-01-31');
        -> -30

 deseo q me den codigos de operaciones matematicas en as400