AWS RDS MySQL - GROUP_CONCAT 返回多行而不是逗号分隔的字符串

Posted 2023-02-24

【中文标题】AWS RDS MySQL - GROUP_CONCAT 返回多行而不是逗号分隔的字符串

【英文标题】：AWS RDS MySQL - GROUP_CONCAT returns multiple rows instead of comma separated string

【发布时间】：2018-10-23 06:57:03

【问题描述】：

我有一个Stored Procedure，它接受三个参数，其中一个是TEXT，它应该包含ids 的逗号分隔值，类似这样-> '12345,54321,11111,22222'，它插入一行数据对于列表中的每个 id。下面是Stored Procedure：

DELIMITER //
-- Create Stored Procedure
CREATE PROCEDURE MyProcedure( 
        IN ItemUUID VARCHAR(255),
        IN ReceiverIds TEXT,
        IN ItemCreated VARCHAR(255)
)

BEGIN
  DECLARE strLen    INT DEFAULT 0;
  DECLARE SubStrLen INT DEFAULT 0;

  IF ReceiverIds IS NULL THEN
    SET ReceiverIds = '';
  END IF;

do_this:
  LOOP
    SET strLen = LENGTH(ReceiverIds);

    INSERT INTO item_receiver (item_uuid, receiver_id, item_created)
    VALUES (ItemUUID ,SUBSTRING_INDEX(ReceiverIds, ',', 1),ItemCreated);

    SET SubStrLen = LENGTH(SUBSTRING_INDEX(ReceiverIds, ',', 1)) + 2;
    SET ReceiverIds = MID(ReceiverIds, SubStrLen, strLen);

    IF ReceiverIds = '' THEN
      LEAVE do_this;
    END IF;
  END LOOP do_this;

END//
DELIMITER ;

要使用ids 获取逗号分隔值，类似这样-> '12345,54321,11111,22222' 我执行subquery，但是，当我调用它Stored Procedure 时出现此错误-> Error Code: 1242. Subquery returns more than 1 row

SET group_concat_max_len = 2048;
call MyProcedure('random_test_uuid',(
    SELECT CAST(GROUP_CONCAT(receiver_id SEPARATOR ',') AS CHAR)  AS receiver_ids FROM receiver
    WHERE user_id LIKE (SELECT user_id FROM user WHERE user_name LIKE 'myName') 
    GROUP BY receiver_id ),
'2017-09-24 23:44:32');

【参考方案1】：

问题是子查询。删除group by:

SELECT CAST(GROUP_CONCAT(receiver_id SEPARATOR ',') AS CHAR)  AS receiver_ids
FROM receiver
WHERE user_id LIKE (SELECT user_id FROM user WHERE user_name LIKE 'myName') 

使用group by，您会为每个receiver_id 获得一个单独的行。 group_concat() 没有做任何事情。

另外，CAST() 是不必要的。这通常会写成：

SELECT GROUP_CONCAT(r.receiver_id SEPARATOR ',') AS receiver_ids
FROM receiver r JOIN
     user u
     ON u.user_id = r.user_id
WHERE u.user_name LIKE 'myName';

如果'myName' 没有使用通配符，那么= 比like 更合适。

如果receiver_id 在receiver 中不是唯一的，那么您可能需要将distinct 添加到group_concat()。