MySQL 1Z0-909 FAQ: Exam Format, Topics, and Prep

Is 1Z0-909 mostly SQL?

Yes, but not only syntax. It is about correctness: NULL semantics, join behavior, grouping, index use, and query-plan reasoning with EXPLAIN.

What’s the highest-yield area?

Joins, aggregation, indexing, and EXPLAIN. If you can predict outputs and spot non-sargable predicates, you will collect a lot of points.

Do I need to memorize every function?

No. Focus on common families: string and date functions, aggregation, and the patterns used with JSON extraction and filtering.

What’s the biggest trap?

Edge cases: NULL in NOT IN, filtering after a LEFT JOIN, and accidentally changing grouping granularity or index usability.

What should I review in the last week?

Focus on:

• join correctness and row multiplication
• NULL predicates and subquery edge cases
• indexing, sargability, and EXPLAIN
• transaction isolation, locking, and stored-program basics

What do strong answers usually avoid?

They avoid choosing the fanciest query or feature. On this exam, the right answer is usually the one that stays correct under edge conditions and works with the optimizer.