MYSQL遊標嵌套循環示例

本文將舉例演示遊標的嵌套用法，首先建造表結構，如下：

drop table if exists `tb_user`;
create table tb_user (
    id bigint(22) not null auto_increment primary key,
    name varchar(20) not NULL,
    age  tinyint(3),
    gmt_create date,
    gmt_modified date
);

drop table if exists `tb_user_param`;
create table tb_user_param (
    id bigint(22) not null auto_increment primary key,
    user_id bigint(22) not null,
    code varchar(100) not null,
    value varchar(1000),
    gmt_create DATE,
    gmt_modified date
);

drop procedure if exists `sp_init_data`;
create procedure `sp_init_data`()
begin
    declare v_i bigint(22) default 0;
    declare v_uid bigint(22);
    declare v_nick varchar(20) default 'lanbo_';
    declare v_code_1 varchar(20) default 'address';
    declare v_code_2 varchar(20) default 'phone';
    declare v_code_3 varchar(20) default 'wangwang_id';
    declare v_value_1 varchar(20) default 'HZ.XiHu';
    declare v_value_2 varchar(20) default '1875757198';
    declare v_value_3 varchar(20) default 'shansun_';

    while v_i < 10 do
        set v_i = v_i + 1;
        insert into tb_user values (null, concat(v_nick, v_i), 23, now(), now());
        select LAST_INSERT_ID() into v_uid;
        insert into tb_user_param values(null, v_uid, v_code_1, v_value_1, now(), now());
        insert into tb_user_param values(null, v_uid, v_code_2, concat(v_value_2, v_i), now(), now());
        insert into tb_user_param values(null, v_uid, v_code_3, concat(v_value_3, v_i), now(), now());
    end while;
    commit;
end;
call sp_init_data();


drop table if exists `tb_key_value`;
create table `tb_key_value`(
    uid bigint(22) not null,
    k varchar(100),
    v varchar(100)
);

我們插入了10條數據到tb_user中，如果tb_user中未定義的字段如address，則放置在tb_user_param中，該表是個key_value的結構，由uid+code定位。

後面我們要做的是，將根據tb_user中的uid找到tb_user_param中相關記錄後，將key_value信息轉移到tb_key_value表中，爲達到演示效果，我們使用嵌套遊標操作數據，代碼如下：

drop procedure if exists `sp_nested_cursor`;
create procedure `sp_nested_cursor`()
begin
    declare v_uid bigint(22);
    declare v_code varchar(100);
    declare v_value varchar(100);
    declare _done TINYINT(1) default 0;
    declare cur_user cursor for select id from `tb_user`;
    declare continue handler for not found set _done = 1;

    open cur_user;
    loop_xxx:loop
        fetch cur_user into v_uid;
        if _done=1 then
            leave loop_xxx;
        end if;
        begin
            declare _inner tinyint(1) default 0;
            declare cur_param cursor for select code, value
                                         from `tb_user_param`
                                         where user_id=v_uid;
            declare continue handler for not found set _inner = 1;
            open cur_param;
            loop_yyy:loop
                fetch cur_param into v_code, v_value;
                if _inner=1 then
                    leave loop_yyy;
                end if;
                insert into tb_key_value values (v_uid, v_code, v_value);
            end loop;
            commit;
        end;
    end loop;
end;
call `sp_nested_cursor`();

 如果想跟蹤上面程序的執行過程，可以藉助MySQL Debugger工具調試學習。

轉載地址： http://shansun123.iteye.com/blog/1026084