SQL · Theory

DATEDIFF()

Theory

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DATEDIFF()

Amit only reaches for DATEDIFF() when Amit walking through DATEDIFF has to stay correct in a small live site.

DATEDIFF() order: meaning → one DATEDIFF step Amit can write from memory → one limit. Dumping ten features helps nobody.

Skip DATEDIFF() and copy-pasting DATEDIFF without a dry-run shows up in a small live site.

DATEDIFF() shows up in a small live site. Name Amit walking through DATEDIFF, not “a real-world scenario”.

DATEDIFF() trap — copy-pasting DATEDIFF without a dry-run. Amit loses marks for that every viva.

After DATEDIFF(), Amit should still remember copy-pasting DATEDIFF without a dry-run.

One breath for DATEDIFF(), then Amit walking through DATEDIFF, then copy-pasting DATEDIFF without a dry-run. Sit down.

Exam tip

For DATEDIFF(): definition + a small live site + one failure.

DATEDIFF() — sample query

-- DATEDIFF()
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;

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

Short notes

DefDATEDIFF() — Amit uses it for Amit walking through DATEDIFF in a small live site.
RuleDATEDIFF() → one DATEDIFF step Amit can write from memory.
RememberDATEDIFF() + the query planner (a small live site).
UseDATEDIFF() in a small live site (Amit walking through DATEDIFF).
TrapDATEDIFF() — copy-pasting DATEDIFF without a dry-run.
ExDATEDIFF() → Amit walking through DATEDIFF.

-- DATEDIFF() 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;

DATEDIFF()

DATEDIFF() — sample query

Short notes

Questions

DATEDIFF()

DATEDIFF() — sample query

Short notes

Questions