SQL · Theory

InnoDB

Theory

369/439

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.

Exam tip

InnoDB for ACID and FOREIGN KEY. Default in MySQL 8.

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.

Short notes

DefInnoDB = default engine, transactions + FKs.
RuleUse InnoDB for real data. Check with SHOW TABLE STATUS.
TrapMyISAM for fees/orders.

SQL · Theory

InnoDB

← All stacks

Theory

369/439

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.

Exam tip

InnoDB for ACID and FOREIGN KEY. Default in MySQL 8.

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.

Short notes

DefInnoDB = default engine, transactions + FKs.
RuleUse InnoDB for real data. Check with SHOW TABLE STATUS.
TrapMyISAM for fees/orders.

InnoDB

InnoDB — sample query

Short notes

Questions

InnoDB

InnoDB — sample query

Short notes

Questions