SQL · Theory

Storage Engines

Theory

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Storage Engines

A storage engine is how the table is stored. SHOW ENGINES; InnoDB is default (transactions, FKs). MyISAM: old, table locks. MEMORY: RAM, lost on restart. CSV: CSV files, little use in apps.

CREATE TABLE … ENGINE=InnoDB; Usually omit it and take the default.

Trap — MEMORY for data you cannot lose. Trap: mixing engines then expecting FKs between them.

On the example next to this theory: Storage Engines: create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Exam tip

InnoDB default. SHOW ENGINES; to list.

Storage Engines — sample query

-- Storage Engines
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;

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

Short notes

DefEngine = storage/locking/transaction style of a table.
RuleInnoDB default. SHOW ENGINES;
TrapMyISAM/MEMORY for important data.

-- Storage Engines 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;

Storage Engines

Storage Engines — sample query

Short notes

Questions

Storage Engines

Storage Engines — sample query

Short notes

Questions