"I hoped (and still hope) that there is something like my beloved SQL*Plus for Oracle that can execute a file with all kinds of SQL Statements."
If you're looking for a simple program that can import a file and execute the SQL statements in it, take a look at DBWConsole (freeware). I have used it to process DDL scripts (table schema) as well as action queries. It does not return data sets so it's not useful for SELECT queries. It supports single line comments prefixed by -- but not multi-line comments wrapped in /* */. It supports command line parameters.
If you want an interactive UI like Oracle SQL Developer or SSMS for Access then Matthew Lock's reference to WinSQL is what you should try.