update join的使用

表一：order
order_id
room_id
company_id

表二：room
room_id
hosue_id

表三：house_company_mapping
house_id
company_id

如上图所示，需要根据house_company_mapping把order表的company_id更新为正确的数据。数据量大概有10W条，肯定是不能通过程序写了，肯定很费时间。于是我采用了存储过程，这个虽然不推荐使用，但是我好像并没有其他好办法。代码如下：

## 公司列表维护数据

DROP PROCEDURE IF EXISTS FountTable;

DELIMITER $$

CREATE PROCEDURE FountTable()

BEGIN

DECLARE v_room_id VARCHAR(32);

DECLARE v_house_id VARCHAR(32);

DECLARE v_company_id VARCHAR(32);

DECLARE v_order_id VARCHAR(32);

#声明游标

    DECLARE cur_FountTable CURSOR FOR SELECT id
                                      FROM
                                       order t
                                      WHERE
                                         company_id = 'a0000000000000000000000000000000'
                                        AND exists(SELECT 1
                                                   FROM house_company_mapping a
                                                   WHERE a.house_id IN (
                                                     SELECT b.house_id
                                                     FROM room b
                                                     WHERE b.id = t.house_id
                                                   ));

DECLARE EXIT HANDLER FOR NOT FOUND CLOSE cur_FountTable;

#打开游标

OPEN cur_FountTable;

REPEAT

FETCH cur_FountTable
INTO v_order_id;

      SELECT room_id
      INTO v_room_id
      FROM order
      WHERE id = v_order_id;

      SELECT house_id
      INTO v_house_id
      FROM room
      WHERE id = v_room_id;

      SELECT ifnull(company_id, 'a0000000000000000000000000000000')
      INTO v_company_id
      FROM house_company_mapping m
      WHERE m.house_id = v_house_id;

      UPDATE order
      SET company_id = v_company_id
      WHERE id = v_order_id;

    UNTIL 0 END REPEAT;
    #关闭游标
    CLOSE cur_FountTable;
  END $$
DELIMITER ;

CALL FountTable();

我尽量让所有的查询和修改都通过索引操作，但是要遍历一个10w条数据的cursor 还是很费时间，大概需要2.5小时。后来知道了update join这种写法，于是我把存储过程改写成了下面这种写法：

UPDATE pay.pay_order a
JOIN (
SELECT
t.id order_id,
b.id house_id,
ifnull(c.company_id, 'a0000000000000000000000000000000') company_id
FROM pay_order t
LEFT JOIN room b
ON t.room_id = b.id
LEFT JOIN house_company_mapping c
ON b.house_id = c.house_id

WHERE t.company_id = 'a0000000000000000000000000000000'
) temp
ON a.id = temp.order_id
SET a.company_id = temp.company_id;

尝试了一下，基本在1分钟内就可以更新完10万条数据。所以推荐还是使用update join这种写法：

update table_a join table_b on a.id=b_id set a.name=b.name where 1=1;

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