SQL · Theory

regexp_instr()

Theory

108/439

regexp_instr()

If you can teach regexp_instr() using a regexp_instr dry-run, you know it. If you only know the heading, you don’t.

regexp_instr() on the board: one regexp_instr step Meera can write from memory. Then say what a regexp_instr dry-run looks like after.

regexp_instr() exists so Meera can keep a regexp_instr dry-run correct in a small live site.

Use regexp_instr() when a regexp_instr dry-run must stay clear. If a simpler SQL step works, use that instead.

If a regexp_instr dry-run breaks under regexp_instr(), check skipping the failure case for regexp_instr first.

Place regexp_instr() next to nearby SQL work — one regexp_instr step Meera can write from memory is the link.

Close regexp_instr() with: “If I skip it, a regexp_instr dry-run goes wrong like this: skipping the failure case for regexp_instr.”

Exam tip

Say regexp_instr() in one breath, then one regexp_instr step Meera can write from memory, then skipping the failure case for regexp_instr.

regexp_instr() — sample query

-- regexp_instr()
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;

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

Short notes

Defregexp_instr() — Meera uses it for a regexp_instr dry-run in a small live site.
Ruleregexp_instr() → one regexp_instr step Meera can write from memory.
Rememberregexp_instr() + an index (a small live site).
Useregexp_instr() in a small live site (a regexp_instr dry-run).
Trapregexp_instr() — skipping the failure case for regexp_instr.
Exregexp_instr() → a regexp_instr dry-run.

-- regexp_instr() 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;

regexp_instr()

regexp_instr() — sample query

Short notes

Questions

regexp_instr()

regexp_instr() — sample query

Short notes

Questions