查看远程分支：
git branch -a
查看本地分支：
git branch
场景：
假如现在远程分支有一个：demo
我们本地没有；
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1.查看远程分支有哪些：
git branch -a
2.然后切换到这个分支：
git checkout remotes/origin/demo
出来了这么一段话：
$ git checkout remotes/origin/demo
Note: checking out 'remotes/origin/demo'.
You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by performing another checkout.
If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -b with the checkout command again. Example:
git checkout -b <new-branch-name>
HEAD is now at 1ad17a6... 演示demo8月12日提交
3.就按照它说的执行：
git checkout -b a
然后就可以了。
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但是，如果执行git pull 会报错，是因为没有和远程分支建立联系（没有跟踪信息）
解决方法：
和远程分支a建立联系：
git branch --set-upstream-to=origin/demo
然后就可以了
git pull