SQL · Theory

IS NULL

Theory

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IS NULL

If you can teach IS NULL using Sara walking through IS NULL, you know it. If you only know the heading, you don’t.

IS NULL order — meaning → one IS NULL step Sara can write from memory → one limit. Dumping ten features helps nobody.

Without IS NULL, a first job task gets messy and Sara walking through IS NULL is hard to trust.

IS NULL shows up in a first job task. Name Sara walking through IS NULL, not “a real-world scenario”.

Don’t do this with IS NULL — skipping the failure case for IS NULL. Interviewers spot it in ten seconds.

Place IS NULL next to nearby SQL work — one IS NULL step Sara can write from memory is the link.

Close IS NULL with: “If I skip it, Sara walking through IS NULL goes wrong like this: skipping the failure case for IS NULL.”

Exam tip

Board: Sara walking through IS NULL. Dry-run IS NULL. Name the trap: skipping the failure case for IS NULL.

IS NULL — sample query

-- IS NULL
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;

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

Short notes

DefIS NULL — Sara uses it for Sara walking through IS NULL in a first job task.
RuleIS NULL → one IS NULL step Sara can write from memory.
RememberIS NULL + the query planner (a first job task).
UseIS NULL in a first job task (Sara walking through IS NULL).
TrapIS NULL — skipping the failure case for IS NULL.
ExIS NULL → Sara walking through IS NULL.

-- IS NULL 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;

IS NULL

IS NULL — sample query

Short notes

Questions

IS NULL

IS NULL — sample query

Short notes

Questions