What is the purpose of starting update project when using idea to operate git?

what"s the difference between these parameters? I feel that update project is of no use.

Idea git java
Mar.11,2021

Thank you for the invitation, starting on the left.
merge: is the merge code for git. The remote code has been modified before you push. You need to merge first. If there is no conflict, the changes are merged automatically, otherwise the code pulled down by
rebase: needs to be merged one by one, but it will not be merged automatically. You need to merge manually

I haven't used the third branch default

using stash: clears stash
the second unused before updating.

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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-64f5-1b36141-2bfed.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b36141-2bfed.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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