it's very strange that so less info about 1Z0-882 in the internets. MySQL is the most popular DB wordwide.
The exam is new. Articles and other info will accumulate over time.
What's the difference to Oracle Database SQL Certified Expert? Which study guide?
There is not an enormous amount in common between the two. The exam does have 14 topic on SQL operations. Since MySQL uses ANSI SQL, What you know from Oracle SQL will be compatible. However, the other 2/3 of the exam has no relationship to 1Z0-047 at all.
No study guides exist for this test yet. Most likely I will write one, but I couldn't give you a time frame. I'm currently working on 1Z0-417. After that I plan to do 1Z0-100. The MySQL exams *might* follow that.
I can't understand that no Third-Party (expect you) is motivated to write a study guide. Why even not Oracle press? Oracle press writes only for DBA, not for dev.
Oracle Press is still a 3rd-party. It's just a differentiated line of books published by McGraw-Hill. It is not Oracle, 'the corporation', publishing the books (although they cooperate with the OPress publisher & authors). For OP to write a book for 1Z0-882, some author has to come forward and propose it to them (and convince them that he is capable of writing a salable book).