SQL · Theory

Date / Time Functions

Theory

213/439

Date / Time Functions

Date / Time Functions is simple if you keep it on paper. Isha uses it for Isha walking through Date / Time Functions in a small live site.

Keep Date / Time Functions small. Isha should finish Isha walking through Date / Time Functions in a few lines, not a 40-line dump.

Without Date / Time Functions, a small live site gets messy and Isha walking through Date / Time Functions is hard to trust.

Use Date / Time Functions when Isha walking through Date / Time Functions must stay clear. If a simpler SQL step works, use that instead.

Date / Time Functions miss: skipping the failure case for Date / Time Functions. Fix it before you talk about advanced SQL.

After Date / Time Functions, Isha should still remember skipping the failure case for Date / Time Functions.

One breath for Date / Time Functions, then Isha walking through Date / Time Functions, then skipping the failure case for Date / Time Functions. Sit down.

Exam tip

Board: Isha walking through Date / Time Functions. Dry-run Date / Time Functions. Name the trap: skipping the failure case for Date / Time Functions.

Date / Time Functions — sample query

-- Date / Time Functions
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;

Date / Time Functions: create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Short notes

DefDate / Time Functions — Isha uses it for Isha walking through Date / Time Functions in a small live site.
RuleDate / Time Functions → one Date / Time Functions step Isha can write from memory.
RememberDate / Time Functions + an index (a small live site).
UseDate / Time Functions in a small live site (Isha walking through Date / Time Functions).
TrapDate / Time Functions — skipping the failure case for Date / Time Functions.
ExDate / Time Functions → Isha walking through Date / Time Functions.

-- Date / Time Functions 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;

Date / Time Functions

Date / Time Functions — sample query

Short notes

Questions

Date / Time Functions

Date / Time Functions — sample query

Short notes

Questions