我得到了这个完美运行的查询:
SELECT FOLDER.folderid, FOLDER.foldername
FROM FOLDER
INNER JOIN COLLABORATORS ON COLLABORATORS.folderid = FOLDER.folderid
WHERE COLLABORATORS.userid = 23
但是当我在 where 子句上添加这个时:“and FOLDER.parent = NULL”它不起作用。完整的查询是:
SELECT FOLDER.folderid, FOLDER.foldername
FROM FOLDER
INNER JOIN COLLABORATORS ON COLLABORATORS.folderid = FOLDER.folderid
WHERE COLLABORATORS.userid = 23 and FOLDER.parent = NULL
有人知道怎么回事吗?谢谢
最佳答案
处理NULL
时, 你不能使用 =
或 <>
因为这些值是未知,而是使用 IS NULL
或 IS NOT NULL
,
WHERE COLLABORATORS.userid = 23 and FOLDER.parent IS NULL
关于mysql - 在 where 子句上查找空值时查询不起作用,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/16073218/