There are differences between the two branches of git, why can't they be merged?

I execute the command:
git diff sub_a master > > diff2.diff
see a lot of differences
I now see that some submission records of master are not merged into sub_a, so I use the above command to compare the next two branches.
I display Already up-to-date when I execute git merge master to merge master into sub_a.
what is the situation and how to solve it?

Git
Mar.20,2021

is your working directory already on master .

git status take a look at what's after On branch .

git merge merges the target branch into the current working branch. If it is already on master , of course it will Already up-to-date.

< hr >

the subject adds that if you make sure the branch is right, it may be a more intelligent situation:

sub_a has been passed by merge, and there is a difference because there is something new on master after merge.

suggest gitk to see if sub_a is under master instead.

it is possible that either the result of the merge has been forgotten, or someone else has merge and failed to tell the subject.

(forgive me, if I keep thinking on the weird side. I have stepped on all these pits. )


has the problem been solved, and how

MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1e425f9-64fc5.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1e425f9-64fc5.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
Need Help?