使用联接的SQL查询更新

Question

这是我的SELECT语句，列出了我要更改的内容；

SELECT

t1.`qid`,
t1.`gid` as 'incorrect gid',
t1.`question` as 'subquestion',
t1.`parent_qid`,

t2.`qid`,
t2.`gid` as 'correct gid',
t2.`question`

FROM `questions` as t1

LEFT JOIN `questions` as t2 ON t1.`parent_qid` = t2.`qid`

WHERE t1.`sid` = '33844' AND t1.`gid` NOT IN ('1306','1317','1319','1320','1321','1322','1323','1324','1325','1326','1327','1328','1329','1330','1331','1332','1333','1334','1335''1334','1335','1336', '1337','1338','1339','1340')

我想使用UPDATE语句将所有“不正确的gid”替换为“正确的gid”。

这是我尝试过的UPDATE语句，但无法正常工作。

UPDATE `questions` as t1 

SET `gid` = t2.`gid`

FROM

`questions` as t1
LEFT JOIN
`questions` as t2 ON t1.`parent_qid` = t2.`qid`

WHERE t1.`sid` = '33844' AND t1.`gid` NOT IN ('1306','1317','1319','1320','1321','1322','1323','1324','1325','1326','1327','1328','1329','1330','1331','1332','1333','1334','1335''1334','1335','1336', '1337','1338','1339','1340')

基本上，所有属于子级的行都具有不正确的gid（组ID），需要进行修复。 但是，所有引用父项的行（因为父项和子项在同一表中）将具有正确的组ID。

因此，我必须将父母groupid加入每个孩子行中。

Answer 1

MySQL中的正确语法：

UPDATE `questions` as t1 LEFT JOIN
       `questions` as t2 ON t1.`parent_qid` = t2.`qid`
    SET t1.`gid` = t2.`gid`
WHERE t1.`sid` = '33844' AND
      t1.`gid` NOT IN ('1306','1317','1319','1320','1321','1322','1323','1324','1325','1326','1327','1328','1329','1330','1331','1332','1333','1334','1335''1334','1335','1336', '1337','1338','1339','1340')