I took the certification before Oracle bought Sun
When the scores of my SCMDBA exams were given (back in August 2007), percentages on the exam were based on information from specfic chapters of the book MySQL 5.0 Certification Study Guide. Oracle has since changed the scoring standard to be the following:
Section 1: Theory, Terminology and Concepts (10%)
Database and Database Objects
Section 2: Data Definition using SQL (25%)
Constraints and Indexes
Section 3: Basic Data Manipulation using SQL (25%)
Recurring SQL Constructs
Section 4: Advanced Data Manipulation using SQL (20%)
Grouping and Aggregate Functions
Section 5: Transactions (10%)
SQL for working with Transaction
Section 6: Import/Export (10%)
Tools for Import/Export
SQL for Import/Export
IMHO, the book I mentioned is the book you should study. Notwithstanding, there is no substitute for experience. So, practice hands-on everything you learn from the book.
As for your question, I took the exam under Pearson VUE. Oracle switched it to Prometric. Just recently, Oracle switched MySQL back to Pearson VUE. The scoring was a fixed number basaed on the random sampling of the questions presented to me.
When I took The first SCMDBA exam (covering chapters 23-25,27-32), I scored 54/46, 46 being the minimum number to pass based on the random sampling of the questions. My second exam score was 47/45 (covering chapters 33-42).
With Oracle's way of doing things and using Pearson VUE, I would expect something like based on the six(6) sections mentioned.