AWS RDS MySQL-GROUP\u CONCAT返回多行,而不是逗号分隔的字符串

我有一个 Stored Procedure 这需要三个参数,其中一个是 TEXT 它应该包含逗号分隔的值 ids ,类似于此-> '12345,54321,11111,22222' ,它将插入一行,其中包含列表中每个id的数据。以下是 存储过程 :

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 ;

获取逗号分隔值的步骤 ids ,类似于此-> '12345543211111122222' 我执行 subquery 然而,当我称之为 存储过程 我收到此错误-> 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');