MySQL Interview Prep

MySQL Interview Topics

• ACID — Atomicity, Consistency, Isolation, Durability — transaction guarantees
• InnoDB vs MyISAM — InnoDB has ACID, FK support, row locking; MyISAM is faster for reads only
• Index types — B-Tree (default), FULLTEXT, HASH (Memory engine), Spatial
• Clustered vs secondary index — InnoDB primary key IS the clustered index (data stored with it)
• N+1 problem — querying DB in a loop; fix with JOIN or eager loading
• EXPLAIN — analyse query execution plan; look for ALL (full scan) and fix with indexes
• Normalisation — 1NF, 2NF, 3NF eliminate redundancy
• LEFT JOIN vs INNER JOIN — LEFT returns all left rows; INNER returns only matches
• GROUP BY vs HAVING — WHERE filters rows before grouping; HAVING filters after
• Replication — primary-replica for read scaling and high availability