PHP + Windows Call to undefined function mysql_connect()

Install WordPress and hits the following error message :

Fatal error: Uncaught Error: Call to undefined function mysql_connect() 
	in C:\nginx-1.12.1\www\wordpress\wp-includes\wp-db.php...

Tested

1. PHP 7.1.10
2. WordPress 4.8.3
3. Nginx 1.12.1
4. MySQL 5.7.17
5. Windows 10

Solution

To install WordPress, PHP needs Mysql extension, to fix this, loads php_mysqli.dll in php.ini file.

; Directory in which the loadable extensions (modules) reside.
; http://php.net/extension-dir
; extension_dir = "./"
; On windows:
; extension_dir = "ext"
extension_dir = "ext"
;extension=php_gmp.dll
;extension=php_intl.dll
;extension=php_imap.dll
;extension=php_interbase.dll
;extension=php_ldap.dll
;extension=php_mbstring.dll
;extension=php_exif.dll      ; Must be after mbstring as it depends on it
extension=php_mysqli.dll
;extension=php_oci8_12c.dll  ; Use with Oracle Database 12c Instant Client
;extension=php_openssl.dll

On Windows, default PHP dll extensions, including php_mysqli.dll are stored in the c:\\your-php-path\\ext folder, make sure the extension_dir path is pointing to the correct folder.

Restart PHP, done.

References

1. PHP php_mysqli.dll
2. PHP extension_dir