【YashanDB知识库】共享从 MySQL异常处理CONTINUE HANDLER的改写方法

MySQL的CONTINUE HANDLER
迁移MySQL业务时，遇到了MySQL的CONTINUE HANDLER FOR not found用法。详情如下：

-- 表DDL

create table t1(c1 int primary key, c2 int);

create table t2(c1 int primary key, c2 int);

-- 数据

insert into t1 values(1,1),(2,2);

insert into t2 values(1,11);

commit;

 

-- 使用CONTINUE HANDLER的存储过程

DELIMITER $$

CREATE PROCEDURE demo(IN p1 int)

BEGIN

    DECLARE s bigint DEFAULT 0;

    DECLARE v1 bigint DEFAULT 0;

    DECLARE v2 bigint DEFAULT 0;

    DECLARE cur1 CURSOR FOR select c2 from t1 where c1=p1;

    DECLARE CONTINUE HANDLER FOR not found SET s=1;

    OPEN cur1;

    r_loop: LOOP

        IF s = 1 THEN

            LEAVE r_loop;

        END IF;

        -- 如果游标fetch结果not found，则设置s=1

        FETCH cur1 INTO v1;

        IF s = 0 THEN

            -- 如果查询结果not found，则设置s=1

            select c2 into v2 from t2 where c1=v1;

            -- 调试：输出v2值

            select v2;

            -- 调试：输出s值

            select s;

        END IF;

    END LOOP r_loop;

    CLOSE cur1;

END$$

DELIMITER ;

执行效果如下：

mysql> CALL DEMO(1);

+------+

| v2 |

+------+

| 11 |

+------+

1 row in set (0.00 sec)

 

+------+

| s |

+------+

| 0 |

+------+

1 row in set (0.00 sec)

 

Query OK, 0 rows affected (0.00 sec)

 

mysql> CALL DEMO(2);

+------+

| v2 |

+------+

| 0 |

+------+

1 row in set (0.00 sec)

 

+------+

| s |

+------+

| 1 |

+------+

1 row in set (0.00 sec)

 

Query OK, 0 rows affected (0.00 sec)

 

mysql> CALL DEMO(3);

Query OK, 0 rows affected (0.00 sec)

YashanDB的改写方法

MySQL的CONTINUE HANDLER需要在YashanDB进行改写。改写原则：1）对于游标的执行，需要使用游标属性%notfound来改写；2）对于select语句的执行，则需要通过NO_DATA_FOUND的异常处理来改写。例如，以上示例的改写详情如下：

CREATE OR REPLACE PROCEDURE demo(p1 IN int) IS

    s bigint DEFAULT 0;

    v1 bigint DEFAULT 0;

    v2 bigint DEFAULT 0;

    CURSOR cur1 is select c2 from t1 where c1=p1;

BEGIN

    OPEN cur1;

    <<r_loop>>

    LOOP

        IF s = 1 THEN

            EXIT r_loop;

        END IF;

        -- 如果游标fetch结果not found，则设置s=1

        FETCH cur1 INTO v1;

        IF cur1%notfound THEN

            s :=1 ;

        END IF;

        IF s = 0 THEN

            -- 如果查询结果not found，则设置s=1

            BEGIN

                select c2 into v2 from t2 where c1=v1;

            EXCEPTION

            WHEN NO_DATA_FOUND THEN

                s :=1 ;

            END;

            -- 调试：输出v2值

            DBMS_OUTPUT.PUT_LINE(v2);

            -- 调试：输出s值

            DBMS_OUTPUT.PUT_LINE(s);

        END IF;

    END LOOP r_loop;

    CLOSE cur1;

END;

/

YashanDB的执行效果
改写后的执行效果如下：

SQL> SET SERVEROUTPUT ON

SQL> CALL DEMO(1);

11

0

 

PL/SQL Succeed.

 

SQL> CALL DEMO(2);

0

1

 

PL/SQL Succeed.

 

SQL> CALL DEMO(3);

 

PL/SQL Succeed.