pip install mysqlclient returns "fatal error C1083: Cannot open file: 'mysql.h': No such file or directory

You can download unofficial windows binaries for your python version using https://www.lfd.uci.edu/~gohlke/pythonlibs/#mysqlclient. Then install it using pip. This way you'll be able to avoid the hassle of dealing with visual studio build tools.

Just download the mysqlclient.whl file most applicable to you. I think in your case it'll be

mysqlclient‑1.3.13‑cp36‑cp36m‑win_amd64.whl

and run

pip install "path to the downloaded .whl file"

This error occurs when trying to install mysqlclient for python32 in 64 bit environments. Uninstall python and re-install 64 bit version. Then pip install mysqlclient will run with no errors.

Well probably,this is one of the stupidest errors i have ever witnessed.
I have Python 3.7.3 32bit along with latest pip3 and i was installing wheels to my Python....and i stumbled on this STUPID error....
Probably my situation is a bit different but you can resolve it just by looking carefully at the error.... at first it seems something is missing and you start blaming you, Windows ,32/64bit and the list goes on and on..
Take a step back...just take a step back and just read the nasty red error message.... read it really well.
In my case it was

ERROR: Command errored out with exit status 1:
     command: 'c:\users\myUserName\appdata\local\programs\python\python37-32\python.exe' -u -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'C:\\Users\\MASTER~1\\AppData\\Local\\Temp\\pip-install-z7x81g2q\\mysqlclient\\setup.py'"'"'; __file__='"'"'C:\\Users\\MASTER~1\\AppData\\Local\\Temp\\pip-install-z7x81g2q\\mysqlclient\\setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' install --record 'C:\Users\MASTER~1\AppData\Local\Temp\pip-record-z1mvci5v\install-record.txt' --single-version-externally-managed --compile
         cwd: C:\Users\MASTER~1\AppData\Local\Temp\pip-install-z7x81g2q\mysqlclient\
    Complete output (30 lines):
    running install
    running build
    running build_py
    creating build
    creating build\lib.win32-3.7
    creating build\lib.win32-3.7\MySQLdb
    copying MySQLdb\__init__.py -> build\lib.win32-3.7\MySQLdb
    copying MySQLdb\_exceptions.py -> build\lib.win32-3.7\MySQLdb
    copying MySQLdb\compat.py -> build\lib.win32-3.7\MySQLdb
    copying MySQLdb\connections.py -> build\lib.win32-3.7\MySQLdb
    copying MySQLdb\converters.py -> build\lib.win32-3.7\MySQLdb
    copying MySQLdb\cursors.py -> build\lib.win32-3.7\MySQLdb
    copying MySQLdb\release.py -> build\lib.win32-3.7\MySQLdb
    copying MySQLdb\times.py -> build\lib.win32-3.7\MySQLdb
    creating build\lib.win32-3.7\MySQLdb\constants
    copying MySQLdb\constants\__init__.py -> build\lib.win32-3.7\MySQLdb\constants
    copying MySQLdb\constants\CLIENT.py -> build\lib.win32-3.7\MySQLdb\constants
    copying MySQLdb\constants\CR.py -> build\lib.win32-3.7\MySQLdb\constants
    copying MySQLdb\constants\ER.py -> build\lib.win32-3.7\MySQLdb\constants
    copying MySQLdb\constants\FIELD_TYPE.py -> build\lib.win32-3.7\MySQLdb\constants
    copying MySQLdb\constants\FLAG.py -> build\lib.win32-3.7\MySQLdb\constants
    running build_ext
    building 'MySQLdb._mysql' extension
    creating build\temp.win32-3.7
    creating build\temp.win32-3.7\Release
    creating build\temp.win32-3.7\Release\MySQLdb
    C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.21.27702\bin\HostX86\x86\cl.exe /c /nologo /Ox /W3 /GL /DNDEBUG /MT -Dversion_info=(1,4,2,'post',1) -D__version__=1.4.2.post1 "-IC:\Program Files (x86)\MySQL\MySQL Connector C 6.1\include\mariadb" -Ic:\users\MyUserName\appdata\local\programs\python\python37-32\include -Ic:\users\MyUserName\appdata\local\programs\python\python37-32\include "-IC:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.21.27702\include" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.17763.0\ucrt" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.17763.0\shared" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.17763.0\um" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.17763.0\winrt" "-IC:\Program Files (x86)\Windows Kits\10\include\10.0.17763.0\cppwinrt" /TcMySQLdb/_mysql.c /Fobuild\temp.win32-3.7\Release\MySQLdb/_mysql.obj /Zl /D_CRT_SECURE_NO_WARNINGS
    _mysql.c
    MySQLdb/_mysql.c(29): fatal error C1083: Cannot open include file: 'mysql.h': No such file or directory
    error: command 'C:\\Program Files (x86)\\Microsoft Visual Studio\\2019\\BuildTools\\VC\\Tools\\MSVC\\14.21.27702\\bin\\HostX86\\x86\\cl.exe' failed with exit status 2
    ----------------------------------------
ERROR: Command errored out with exit status 1: 'c:\users\MyUserName\appdata\local\programs\python\python37-32\python.exe' -u -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'C:\\Users\\MASTER~1\\AppData\\Local\\Temp\\pip-install-z7x81g2q\\mysqlclient\\setup.py'"'"'; __file__='"'"'C:\\Users\\MASTER~1\\AppData\\Local\\Temp\\pip-install-z7x81g2q\\mysqlclient\\setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' install --record 'C:\Users\MASTER~1\AppData\Local\Temp\pip-record-z1mvci5v\install-record.txt' --single-version-externally-managed --compile Check the logs for full command output.

Have you read it well ?...i assume that you have everything ... the Build tools, the MySQL Connector C 6.1...you even moved it to Program Files (x86)...so what it wrong...?? ...
Now take a closer look

C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.21.27702\bin\HostX86\x86\cl.exe /c /nologo /Ox /W3 /GL /DNDEBUG /MT -Dversion_info=(1,4,2,'post',1) -D__version__=1.4.2.post1 "-IC:\Program Files (x86)\MySQL\MySQL Connector C 6.1\include\mariadb" -

I am pretty sure you saw it...STILL NO ?.... let me bold it for you

"-IC:\Program Files (x86)\MySQL\MySQL Connector C 6.1\include\mariadb" -

mariadb
Well it can't be any stupidest than this ...the installer looks for mariadb includes and later libs Just go to the mariadb site and download the MariaDB C/C++ connector and install it...
Well its not over.. Goto to C:\Program Files (x86)\MySQL\MySQL Connector C 6.1\include and create folder mariadb...and copy paste the contents from the mariaDb connector installation include folder
again don't go way...go to C:\Program Files (x86)\MySQL\MySQL Connector C 6.1\lib and do again the same drill for the lib folder
so you should have

C:\Program Files (x86)\MySQL\MySQL Connector C 6.1\include\mariadb  

C:\Program Files (x86)\MySQL\MySQL Connector C 6.1\lib\mariadb  

Now hit the pip3 install mysqlclient
and enjoy installing without a nag...the end

Successfully installed mysqlclient-1.4.2.post1

I had this issue (exactly same error) and tried all the solutions mentioned above, and neither of them worked (at least for me), actually I was about to pull my hairs over this issue till I found the solution in a very weird, simple and stupid way!! .

I did the following steps so that the problem solved and life got sweet again.

First I installed MySQL Connector/C from here

Second (after installation finished) I copied MySQL Connector C 6.1 folder from Program files/MySQL into Program files (x86)/MySQL

note that you might have to create MySQL folder if it doesn't exist in Program files (x86) (it didn't exist for me)

As simple as that, it worked for me, it seems for some (or all) 64-bit windows, pip or more probably mysqlclient setup script only searches Program files (x86) folder for some MySQL files (such as 'mysql.h') and doesn't search Program files and since doesn't find anything in Program files (x86) raises the error very dumb!!! isn't it