Currently in my system I have installed Oracle PL/SQL. In addition to this, I am now thinking of installing MySQL. Is there any known issue in running both these databases on the same machine? I hope someone can advise or share their experience. Thanks.
"PL/SQL" is simply the proprietary procedural extension to SQL that runs inside Oracle's RDBMS i.e. it is a programming language, not the database.
You should have no problems running MySQL and Oracle on the same machine, although it will depend on your RAM and processor. Oracle and MySQL listen on different standard ports for connections, so it is perfectly possible to have separate sessions running against each database without conflict.