MySQL 1Z0-909 exam guide covering schema design, SQL development, indexing, performance, and deployment decisions.
1Z0-909 is a SQL and schema-design correctness exam. Strong answers usually come from reading joins, grouping, indexes, and transaction behavior precisely rather than choosing the query that merely sounds reasonable.
Sargable predicate: A condition the optimizer can use efficiently with an index instead of forcing a broader scan.
Transaction isolation: The rule set that controls what one transaction can see from another transaction’s work.
What this guide emphasizes
query correctness and NULL edge cases
joins, aggregation, and schema design choices
indexes, EXPLAIN, and optimizer-aware reasoning
transactions, locking, stored programs, and JSON usage
What strong answers usually do
trace row count changes before trusting grouped or filtered output
match index and EXPLAIN decisions to the actual predicate shape
treat transaction and locking behavior as correctness questions, not trivia
prefer the simplest query or schema choice that preserves correctness and performance