You need to create an entity relationship diagram (ERD) from the Oracle database first. If you download and use a trial version of ERwin Studio, you can reverse engineer the Oracle database, and ERwin Studio will help you to convert the schema to MYSQL. Then you just need to create a database link from either the Oracle database or the MYSQL database to the other database and copy the data across. You probably want to create the schema without constraints or indexes first, move the data, then add the missing constraints and data. you will likely need several attempts at this fixing things as you go.
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