This conflict is caused by this commit:
https://github.com/mariadb-corporation/mariadb-connector-c/commit/be86fb461d9dfc514a8e37830b6045fc5a253511

We remove the libraries in mariadb package to prevent conflicts with connector-c's libraries, so I've included this library to the delete list too, and it should solve this problem
Currently building the mariadb-3:10.4.12-6 which contains this change.

That does indeed appear to fix the conflict.  Thanks.

This is a problem in F32 as well.

Hi Erik,

Please can you tell me what version of mariadb and mariadb-connector-c are you using?

You can use this commads:
rpm -qa mariadb
rpm -qa mariadb-connector-c

Thank you

[erik@Erik-PC ~]$ rpm -qa mariadb
mariadb-10.4.13-1.fc32.x86_64
[erik@Erik-PC ~]$ rpm -qa mariadb-connector-c
mariadb-connector-c-3.1.8-1.fc32.x86_64

And what is the exact problem here?

I've just tried to install mariadb-10.4.13 with mariadb-connector-c-3.8.1 and everything went successfully.

The problem was as I described in fedora user mailing list:

After dnf system-upgrade download --releasever=32 I get the following error:

the file /usr/include/mysql/mariadb_rpl.h makes conflict between the attempted
installation of mariadb-devel-3:10.4.12-3.fc32.x86_64 and mariadb-connector-c-devel-3.1.8-1.fc32.x86_64

The original error message was in Danish but I have attempted to translate it as well as I could. I hope it is understood.

Removing mariadb-devel made the system-upgrade run successfully.

Yes thanks for investigation, I've tried manually install version 10.4.12-3 and it failed.

It's weird that this version is being installed when version 10.4.13 is default for f32.

I will look into that and give you update as soon as possible.

I think I see the problem.

Did you upgraded the packages before fedora upgrade?
Using: sudo dnf upgrade --refresh

It's recommended to do before upgrading OS.

Here is the fedora-magazine guide to upgrade fedora 31 to 32:
https://fedoramagazine.org/upgrading-fedora-31-to-fedora-32/

Yes, I did upgrade --refresh before system-upgrade. I think the problem was mariadb-devel and since I don't use it, it was safe to remove it.

Okay, I will try to reproduce it.

So IIRC you had Fedora 31 installed with mariadb-devel and mariadb-connector-c-devel packages installed.

Then you followed these steps:
1) sudo dnf upgrade --refresh (Updated all packages)
2) sudo dnf install dnf-plugin-system-upgrade (Install dnf plugin)
3) sudo dnf system-upgrade download --releasever=32 (Tried to install Fedora 32, but it failed here!)

Is my estimation correct?

Yes, that is correct.

I've created a new Fedora 31 machine with mariadb-devel and mariadb-connector-c-devel packages installed (conflicting ones),
and followed steps mentioned above.

Everything went smooth, so I can't see why did you had the conflict problem.

If anyone reading this have the same problem please add comment here and I will give this one another look, but for now I think it's fixed.

I am experiencing this in F31 now:

rpm -qa mariadb
mariadb-10.3.22-1.fc31.x86_64

rpm -qa mariadb-connector-c
mariadb-connector-c-3.1.9-5.fc31.x86_64

The problem appears when I try to install mariadb-devel:
Error: Transaction test error:
  file /usr/include/mysql/mariadb_rpl.h from install of mariadb-devel-3:10.3.22-1.fc31.x86_64 conflicts with file from package mariadb-connector-c-devel-3.1.9-5.fc31.x86_64

Thanks for reporting.

I've already started a build for it.

I'll link the update to this BZ for you to know when it's done

The tracking will be in BZ#1876012

I apologize for the confusion

I am experiencing the same results as reported in comment 14 but in F32.
An attempt to update fails with 
Transaction test error:  file /usr/include/mysql/mariadb_rpl.h  etc.

Hi Roger,

We should lead this conversation only in one BZ.

My answer is in BZ#1876012

Thank you for understanding.
Lukas