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

Question

我有一个 Stored Procedure 接受三个参数，其中一个是 TEXT 并且它应该包含用 ids 逗号分隔的值，像这样 -> '12345,54321,11111,22222'，这会为列表中的每个 id 插入一行数据。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，当我调用此 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');

Answer 1

问题出在子查询上。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')

对于 group by，每个 receiver_id 都有单独的一行。 group_concat() 没有做任何事情。

此外，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'不使用通配符，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()。

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

AWS RDS MySQL - GROUP_CONCAT returns multiple rows instead of comma separated string

mysql

sql

stored-procedures

subquery

group-concat