UPDATE project_file set file = null where id = 7 结果为:空(null) 不是字符串'null'
UPDATE project_file set file = 'null' where id = 7 结果为:'null' 是字符串
UPDATE project_file set file is null where id = 7 报错
UPDATE project_file set file = null where id = 7 结果为:空(null) 不是字符串'null'
UPDATE project_file set file = 'null' where id = 7 结果为:'null' 是字符串
UPDATE project_file set file is null where id = 7 报错
一. 二. 三. ! 作 者 : Yaopengfei(姚鵬飛) 博客地址 : http://www.cnblogs.com