Merge vs squash vs rebase on GitHub, explained

Alex Tutor

News on the finance request. Daniel's pull request #133, "Raise free-delivery threshold to 1000 UAH", has been approved in review. One thing is left: merging it.

Daniel

That title is your commit message from module 1, by the way. I liked the summary line, so I reused it for the pull request.

You

My words in the history of the site. I could get used to that.

Alex Tutor

Merging means bringing the changes of one branch into another. Here: from feature/free-delivery-1000 into main. Until that happens, the site keeps saying 800.

Alex Tutor

Pull request #133 before the mergeThree commits on the branch, none of them in main yet.

8be2f70Add cat treats bundlemain
5c1d7e2Set freeDeliveryFrom to 1000
a8f40b9Update delivery page text
d36b9c5Update cart hint textfeature/free-delivery-1000

You

Three commits on the branch and none of them in main. Three ahead, zero behind: main hasn't moved since Daniel started.

Alex Tutor

After the merge main will contain all three changes: the new number in the config, the delivery page text and the hint in the cart. The branch itself stays as it was.

Alex Tutor

Question 1

Daniel merges feature/free-delivery-1000 into main. What changes?

Choose one answerThe branch receives the changes from main; main stays as it wasBoth branches are deleted and replaced by a new onemain receives the branch's changes; the branch itself stays as it wasOnly the config file moves; text files have to be merged separately

Alex Tutor

At the bottom of the pull request there is a green button, Merge pull request, with a small arrow next to it. The arrow opens three options.

You

Create a merge commit, Squash and merge, Rebase and merge. Which one gives the right result?

Alex Tutor

All of them. After any of the three, the files in main are identical: the threshold is 1000 either way. What differs is the history you'll read afterwards.

You

Then how does anyone choose?

Daniel

Which options you see depends on the repository settings. An admin can switch any of them off, so some repositories offer only one.

Alex Tutor

Let's take them one by one, on the same branch, and draw what main looks like afterwards.

Alex Tutor

Question 2

The three options in GitHub's merge button leave different text in the files of main.

TrueFalse

Alex Tutor

Option one, Create a merge commit. GitHub adds the branch's commits to main as they are and ties the two lines together with one extra commit, a merge commit.

Alex Tutor

Option 1: a merge commitThe two lanes join in e4b7a90, which has two parents. The history of main gains four entries.

8be2f70Add cat treats bundle
5c1d7e2Set freeDeliveryFrom to 1000
a8f40b9Update delivery page text
d36b9c5Update cart hint textfeature/free-delivery-1000
e4b7a90Merge pull request #133main

You

The two lanes join in e4b7a90. So that commit has two parents: the previous commit on main and the last one on the branch.

Alex Tutor

Right. Its message is written by GitHub: "Merge pull request #133 from catchow/feature/free-delivery-1000". The history of main grows by four entries: Daniel's three commits and the merge commit.

Daniel

In the terminal engineers do the same with git merge. Nothing is rewritten: my commits keep their hashes, and you can always see where a branch started and where it came back.

You

And the price is a busier history: every small step of every branch ends up in main.

Alex Tutor

Question 3

Pull request #140 was merged with Create a merge commit. Which statements are true? Select all that apply.

Pull request #140 merged with a merge commit

r1Add returns page
t1Add returns form
t2Validate order numberfeature/returns-form
r2Fix typo on returns page
r3Merge pull request #140main

Choose all that applyt1 and t2 are now part of main's history with their original hashesr3 has two parents: r2 and t2main gained exactly one new entry in its historyThe branch's commits were combined into onemain's history gained three entries: t1, t2 and r3

Alex Tutor

Option two, Squash and merge. GitHub takes all the changes from the branch and puts them into main as one new commit.

Alex Tutor

Option 2: squash and mergeOne new commit on main, 6f2c8a1, with a dashed link to the branch. The three original commits are not in the history of main.

8be2f70Add cat treats bundle
5c1d7e2Set freeDeliveryFrom to 1000
a8f40b9Update delivery page text
d36b9c5Update cart hint textfeature/free-delivery-1000
6f2c8a1Raise free-delivery threshold to 1000 UAH (#133)main

You

One commit, 6f2c8a1, and a dashed line instead of a solid one. And its title ends with (#133).

Alex Tutor

Dashed, because Daniel's three commits did not become part of main's history. Their changes did, packed into one commit. GitHub adds the pull request number to its title by itself.

Daniel

Before confirming, GitHub lets me edit that commit's message. By default it takes the pull request title and lists my three commit titles underneath, so nothing is really lost.

This is what our team uses. That's why main in module 1 looked like a straight line: one pull request, one commit. My "oops, typo" commits never get there.

You

And if I want to see the three original steps?

Alex Tutor

Open the pull request. Its Commits tab keeps them, even after the branch has been deleted.

Alex Tutor

Question 4

Pull request #140 was merged with Squash and merge. How many new commits did main get, and where can t1 and t2 still be seen?

Pull request #140 merged with squash

r1Add returns page
t1Add returns form
t2Validate order numberfeature/returns-form
r2Fix typo on returns page
r3Add returns form (#140)main

Choose one answerOne (r3); t1 and t2 stay visible in the pull request's Commits tabTwo (t1 and t2); r3 is only a name for the pairThree (t1, t2 and r3)One (r3); t1 and t2 are deleted from GitHub for good

Alex Tutor

Option three, Rebase and merge. GitHub replays the branch's commits on top of main, one by one. No merge commit and no squashing.

Alex Tutor

Option 3: rebase and mergeThree copies of the commits, with new hashes, continue the straight line of main. The originals stay on the branch until it is deleted.

8be2f70Add cat treats bundle
5c1d7e2Set freeDeliveryFrom to 1000
a8f40b9Update delivery page text
d36b9c5Update cart hint textfeature/free-delivery-1000
1f6a3d8Set freeDeliveryFrom to 1000
2b9e5c4Update delivery page text
7d0c8f1Update cart hint textmain

You

Three commits on main with the same messages as on the branch, but different hashes.

Alex Tutor

Because they are copies. Rebase re-creates each commit in a new place, and a re-created commit gets a new hash. The history stays a straight line and keeps every step.

Daniel

You'll also hear "fast-forward". If main hasn't changed since the branch started, there is nothing to combine. Git can simply move the name main forward to the last commit of the branch.

You

Like our case: main stood still while you worked. No new commit at all, just the name catching up.

Daniel

Yes, but that's a terminal thing. As of 2026 GitHub's button doesn't do a plain fast-forward: the first option always adds a merge commit, and the third always re-creates the commits.

Alex Tutor

Question 5

Match each way of merging with what the graph looks like afterwards.

Tap an answer, then tap the row it belongs to. You can also drag.

Create a merge commit
Squash and merge
Rebase and merge
Fast-forward in the terminal

Answers left to place

You

If the files end up the same, why do teams argue about this?

Daniel

Because we read history every day. With squash, each line in main is one finished piece of work with a link to its pull request. Reverting it is one click.

Teams that choose merge commits want the full record: every commit with its original hash and the exact points where branches joined. Rebase fans want every step too, but in a straight line.

Alex Tutor

There is no winner. What matters is that the team agrees on one way, so the history reads the same from week to week.

For you it means: look at the graph before you count. In a squash repository one commit can hide a week of work. In a merge-commit repository ten commits can be one small feature.

You

So "how many commits went into this release?" is a trick question until I know how the team merges.

Alex Tutor

Question 6

Which merge option produced this history of main?

Pull request #140 after the merge

r1Add returns page
t1Add returns form
t2Validate order numberfeature/returns-form
r2Fix typo on returns page
r3Add returns form
r4Validate order numbermain

Choose one answerCreate a merge commitRebase and mergeSquash and mergeThe branch was deleted without merging

Alex Tutor

Daniel pressed Squash and merge, then Confirm squash and merge. Now the question you'll hear most often as a PM: is the change in?

Look at the badge at the top of the pull request. Green Open has turned into purple Merged, and the line next to it says the commit went into main.

Alex Tutor

Pull requests in catchow/website

Raise free-delivery threshold to 1000 UAH#133
Merged into main today: the changes are in main
Rewrite delivery page copy#132
Open: Emma's changes are still on her branch
Fix checkout button after cart edits#134
Draft: Daniel is still working on it

You

So #133 is in main. Emma's #132 is still open, and the checkout fix, #134, is only a draft. Neither of those has reached main.

Alex Tutor

Two more checks. First, read which branch it was merged into: a pull request can target a branch other than main. Second, merged doesn't mean released.

Daniel

At CatChow a merge into main is deployed automatically within minutes. Other teams collect merges and ship them as a release. We'll get there in module 4.

And remember my button. Pull request #97 still says Merged, although #98 reverted it ten minutes later. Merged is a fact about the past. When in doubt, open the file in main.

You

So three questions every time: merged into what, when, and is it still there.

Alex Tutor

Question 7

Which of these pull requests have their changes in main right now? Select all that apply.

Recent pull requests in catchow/website

Add summer promo banner#129
Rewrite delivery page copy#132
Raise free-delivery threshold to 1000 UAH#133
Fix checkout button after cart edits#134
Try animated delivery badge#127

Choose all that apply#129 "Add summer promo banner"#132 "Rewrite delivery page copy"#133 "Raise free-delivery threshold to 1000 UAH"#134 "Fix checkout button after cart edits"#127 "Try animated delivery badge"

Alex Tutor

Last one. A colleague from analytics opened pull request #133 and is confused: the pull request lists three commits, but the history of main shows only one.

You

And they're sure two commits got lost on the way.

Alex Tutor

Explain in two or three sentences what happened and where the three commits can still be found.

Daniel

Bonus point if you mention the number in the commit title. It's the fastest way back to the pull request.

Alex Tutor

Question 8Short answer · AI-checked task

A colleague opened pull request #133 and sees three commits in its Commits tab, but the history of main shows only one: "Raise free-delivery threshold to 1000 UAH (#133)". They think two commits were lost. Explain in 2–3 sentences what happened and where the three commits can still be found.

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Next lesson: Emma's pull request. She and Daniel changed the same line on the delivery page, and GitHub refuses to merge it on its own.

You

A conflict. The word alone sounds like trouble.

Alex Tutor

That’s the lesson. You answered every task — nicely done.

Next lesson: Merge conflicts: why they happen and what to do