mysql 游标使用

请使用 mysql 1.5 或以上version;

测试表 level ;

create table test.level (name varchar(20));

 

 再 insert 些数据 ;

 

 /*初始化*/ 
 drop procedure if exists  useCursor // 
   
 /*建立 存储过程 create */ 
 CREATE PROCEDURE useCursor()
    BEGIN
    /*局部变量的定义 declare*/ 

         declare tmpName varchar(20) default '' ;

         declare allName varchar(255) default '' ;

         declare cur1 CURSOR FOR SELECT name FROM test.level ;

         /*    mysql 不知道为什么用异常加入判断 ？

          *    此请参考官方文档 20.2.11. 光标 光标 

          *        这把 游标 异常后 捕捉 

          *        并设置 循环使用 变量 tmpname 为 null 跳出循环。

          */

         declare CONTINUE HANDLER FOR SQLSTATE '02000' SET tmpname = null;
  

    /*开游标*/ 

     OPEN cur1;

         /*游标向下走一步*/ 

         FETCH cur1 INTO tmpName;

         /* 循环体 这很明显 把游标查询出的 name 都加起并用 ; 号隔开 */

      WHILE ( tmpname is not null) DO

          set tmpName = CONCAT(tmpName ,";") ;

          set allName = CONCAT(allName ,tmpName) ;

        /*游标向下走一步*/ 

        FETCH cur1 INTO tmpName;

      END WHILE;

      CLOSE cur1;


    select allName ;

END;//

call useCursor()//

 

 

运行结果：

 

mysql> call useCursor()//

+--------------------------------------+

| allName                              |

+--------------------------------------+

| f1;c3;c6;c5;c2;c4;c1;f1;f3;f4;f2;f5; |

+--------------------------------------+

1 row in set (0.00 sec)

 

 

DELIMITER $$  
  
DROP PROCEDURE IF EXITS cursor_example$$  
CREATE PROCEDURE cursor_example()  
     READS SQL DATA  
BEGIN  
     DECLARE l_employee_id INT;  
     DECLARE l_salary NUMERIC(8,2);  
     DECLARE l_department_id INT;  
     DECLARE done INT DEFAULT 0;  
     DECLARE cur1 CURSOR FOR SELECT employee_id, salary, department_id FROM employees;  
     DECLARE CONTINUE HANDLER FOR NOT FOUND SET done=1;  
  
     OPEN cur1;  
     emp_loop: LOOP  
         FETCH cur1 INTO l_employee_id, l_salary, l_department_id;  
         IF done=1 THEN  
             LEAVE emp_loop;  
         END IF;  
     END LOOP emp_loop;  
     CLOSE cur1;  
END$$  
DELIMITER ;  

 

/*创建过程*/
DELIMITER //
DROP PROCEDURE IF EXISTS test //
CREATE PROCEDURE test()
BEGIN
    DECLARE done INT DEFAULT 0;
    DECLARE a VARCHAR(200) DEFAULT '';
    DECLARE c VARCHAR(200) DEFAULT '';
    
    DECLARE mycursor CURSOR FOR SELECT  fusername FROM uchome_friend;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done=1;
    
    OPEN mycursor;
    
    REPEAT 
        FETCH mycursor INTO a;
        IF NOT done THEN
            SET c=CONCAT(c,a);/*字符串相加*/
        END IF;
        
    UNTIL done END REPEAT;
    
    CLOSE mycursor;
    
    SELECT c;
END //
DELIMITER ;