我有3列：( ToDate , FromDate , Diff ) .
我想自动添加一个值到 Diff 之间有差异的列 ToDate 以及 FromDate ，并希望将其保存到表中。
我可以手动创建临时 Diff 列使用 SELECT ToDate,FromDate, (TO_DAYS(FromDate) - TO_DAYS(ToDate)) AS Diff FROM tbl_name ,
但不会保存到 Diff 柱
所以我最后键入： INSERT INTO tbl_name (Diff) SELECT (TO_DAYS(FromDate) - TO_DAYS(ToDate)) AS Diff FROM tbl_name 我想要这样的东西：

FromDate  
2018-05-22

ToDate    
2018-05-23

Diff

1