SQL · Theory

IFNULL()

Theory

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IFNULL()

IFNULL() is simple if you keep it on paper. Ananya uses it for a IFNULL dry-run in a campus project.

IFNULL() on the board — one IFNULL step Ananya can write from memory. Then say what a IFNULL dry-run looks like after.

IFNULL() exists so Ananya can keep a IFNULL dry-run correct in a campus project.

Ananya ships IFNULL() in a campus project. That is the use case worth saying.

Don’t do this with IFNULL() — copy-pasting IFNULL without a dry-run. Interviewers spot it in ten seconds.

IFNULL() is not a lonely heading. Ananya ties it to a IFNULL dry-run.

Viva for IFNULL(): what it is → one IFNULL step Ananya can write from memory → the mistake (copy-pasting IFNULL without a dry-run).

Exam tip

Board: a IFNULL dry-run. Dry-run IFNULL(). Name the trap: copy-pasting IFNULL without a dry-run.

IFNULL() — sample query

-- IFNULL()
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;

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

Short notes

DefIFNULL() — Ananya uses it for a IFNULL dry-run in a campus project.
RuleIFNULL() → one IFNULL step Ananya can write from memory.
RememberIFNULL() + InnoDB (a campus project).
UseIFNULL() in a campus project (a IFNULL dry-run).
TrapIFNULL() — copy-pasting IFNULL without a dry-run.
ExIFNULL() → a IFNULL dry-run.

-- IFNULL() 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;

IFNULL()

IFNULL() — sample query

Short notes

Questions

IFNULL()

IFNULL() — sample query

Short notes

Questions