基于MySQL游标的具体使用详解

测试表 level ;

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

再 insert 些数据 ;

代码

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 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MySQL 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;  

结束循环体:

END WHILE;  

关闭游标

CLOSE cur1;  

选择数据

select allName ;  

结束存储过程

END;//  

调用存储过程：

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)  

loop循环游标：

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 ;  

repeat循环游标：

/*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 ;  

/*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 ;  

原文出处：teakki -> https://www.teakki.com/p/57e22e01a16367940da63f6c