How to Set Default Limit in Store Procedure in SQL

This is stored procedure which show you rows return as per mention in stored procedure.

 CREATE PROCEDURE get_categories(  
 IN p_action_flag VARCHAR(50),  
 IN p_firstrow int,  
 IN p_lastrow int)  
 BEGIN  
 IF p_action_flag = 'all'  
 THEN  
 SELECT top 50 u.*, d.name, d.image FROM user u, member gu, detail d  
 WHERE u.user_id = gu.user_id AND u.user_id = d.user_id AND u.status = '1'  
 AND gu.group_id IN (1, 7) GROUP BY u.user_id ORDER BY d.name LIMIT p_firstrow,p_lastrow;  
 ELSEIF p_action_flag = 'Most Viewed'  
 THEN  
 SELECT top 50 u.*, d.name, d.image FROM user u, member gu, detail d WHERE u.user_id = gu.user_id AND u.user_id = d.user_id AND u.status = '1' AND gu.group_id IN (1, 7)  
 GROUP BY u.user_id ORDER BY u.views DESC, d.name ASC LIMIT p_firstrow,p_lastrow ;  
 END IF  
 END