.htaccess - How do we program such PHP scripts? -

sometimes see websites contain urls these:

somesite.com/123.php

somesite.com/124.php

somesite.com/125.php

the numbers before '.php' ids of mysql query

somesite.com/123.php = somesite.com/file.php?id=123.

i noticed these file [123.php,124.php,125.php] not stored in server.

how can ?

...using rewriting rules apache, placed in .htaccess files.