我希望使用另一个表中的数据更新空字段

Question

我使用SELECT COUNT（*）检查我的WHERE语句并获得了正确的更新次数，但是当我尝试UPDATE时，我在第3行遇到语法错误。

UPDATE scans AS s
SET s.sbjnum = d.sbjnum
JOIN details AS d on d.name = s.name
WHERE s.sbjnum =''

Answer 1

您必须拥有FROM才能拥有JOIN

UPDATE scans 
SET sbjnum = d.sbjnum 
FROM scans s
JOIN details AS d ON d.name = s.name 
WHERE s.sbjnum =''

根据MySQL手册，您可以这样写：

UPDATE scans AS s
JOIN details AS d ON d.name = s.name 
SET sbjnum = d.sbjnum 
WHERE s.sbjnum =''