InnoDB — SQL Technical Interview Questions & Answers

InnoDB

InnoDB

  • InnoDB is the default storage engine. It gives transactions (COMMIT/ROLLBACK), FOREIGN KEYs, and crash recovery. This is the engine you want for students, fees, orders.
  • MyISAM is older: table-level locks, no transactions, no FKs. Full-text search was its old selling point — InnoDB has fulltext now too.
  • SHOW TABLE STATUS; Engine column. ALTER TABLE t ENGINE=InnoDB; to convert (backup first).
  • Trap: creating MyISAM tables in 2026 and promising ACID.
  • On the example next to this theory: InnoDB: create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Technical Interview Tip: InnoDB for ACID and FOREIGN KEY. Default in MySQL 8.

Code Examples for InnoDB

InnoDB — sample query

-- InnoDB
CREATE TABLE demo (
  id INTEGER PRIMARY KEY,
  label TEXT NOT NULL,
  qty INTEGER DEFAULT 0
);
INSERT INTO demo (id, label, qty) VALUES
  (1, 'alpha', 2),
  (2, 'beta', 5);
SELECT label, qty FROM demo WHERE qty >= 2 ORDER BY qty DESC;

InnoDB: create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

How to Explain InnoDB to an Interviewer

Why InnoDB?

Transactions Foreign keys Crash-safe