我试过两种方法。首先，只是引用回它自己作为子选择，然后我尝试创建一个临时表，加载所需的数据，然后从临时表中选择子选择。两者都不起作用。

UPDATE t_call_details cd,
(SELECT 
    sessionid,
        GROUP_CONCAT(dir
            ORDER BY call_start
            SEPARATOR '|') AS gc_dir
FROM
    t_call_details
GROUP BY sessionid) AS gc 
SET 
cd.overall_calldirection = gc.gc_dir
WHERE
cd.sessionid = gc.sessionid
    AND ISNULL(cd.overall_calldirection)

接下来我试着。。。

CREATE TEMPORARY TABLE temp_t_call_details LIKE t_call_details;

INSERT INTO temp_t_call_details (id, sessionid, dir) SELECT id, sessionid, dir from t_call_details where isnull(t_call_details.overall_calldirection);

UPDATE t_call_details cd,
(SELECT 
    sessionid,
        GROUP_CONCAT(dir
            ORDER BY call_start
            SEPARATOR '|') AS gc_dir
FROM
    temp_t_call_details
GROUP BY sessionid) AS gc 
SET 
cd.overall_calldirection = gc.gc_dir
WHERE
cd.sessionid = gc.sessionid
    AND cd.year = 2018
    AND ISNULL(cd.overall_calldirection);

我刚收到错误代码：2013。在每次超过600秒的查询过程中与mysql服务器失去连接。我认为我的代码是准确的；应该有用。是否有一个超时我错过了，我需要更新到一个更大的数字？