SQL · Theory

Account Lock

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Account Lock

Meera only reaches for Account Lock when average per subject has to stay correct in a report.

For Account Lock, InnoDB is in play. Don’t blame it until you have traced average per subject.

Skip Account Lock and SELECT extra column not in GROUP BY shows up in a report.

Account Lock shows up in a report. Name average per subject, not “a real-world scenario”.

Don’t do this with Account Lock — SELECT extra column not in GROUP BY. Interviewers spot it in ten seconds.

Place Account Lock next to nearby SQL work — GROUP BY subject is the link.

One breath for Account Lock, then average per subject, then SELECT extra column not in GROUP BY. Sit down.

Exam tip

For Account Lock: definition + a report + one failure.

Account Lock — sample query

-- Account Lock
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;

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

Short notes

DefAccount Lock — Meera uses it for average per subject in a report.
RuleAccount Lock → GROUP BY subject.
RememberAccount Lock + InnoDB (a report).
UseAccount Lock in a report (average per subject).
TrapAccount Lock — SELECT extra column not in GROUP BY.
ExAccount Lock → average per subject.

-- Account Lock 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;

Account Lock

Account Lock — sample query

Short notes

Questions

Account Lock

Account Lock — sample query

Short notes

Questions