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SUBSTR()()

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SUBSTR()()

SUBSTR()() sits in lab hour. Dev’s job is Dev walking through SUBSTR. Write that first.

Keep SUBSTR()() small. Dev should finish Dev walking through SUBSTR in a few lines, not a 40-line dump.

Without SUBSTR()(), lab hour gets messy and Dev walking through SUBSTR is hard to trust.

Use SUBSTR()() when Dev walking through SUBSTR must stay clear. If a simpler SQL step works, use that instead.

SUBSTR()() miss — skipping the failure case for SUBSTR. Fix it before you talk about advanced SQL.

After SUBSTR()(), Dev should still remember skipping the failure case for SUBSTR.

Close SUBSTR()() with: “If I skip it, Dev walking through SUBSTR goes wrong like this: skipping the failure case for SUBSTR.”

Exam tip

Board: Dev walking through SUBSTR. Dry-run SUBSTR()(). Name the trap: skipping the failure case for SUBSTR.

SUBSTR()() — sample query

-- SUBSTR()()
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;

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

Short notes

DefSUBSTR()() — Dev uses it for Dev walking through SUBSTR in lab hour.
RuleSUBSTR()() → one SUBSTR step Dev can write from memory.
RememberSUBSTR()() + an index (lab hour).
UseSUBSTR()() in lab hour (Dev walking through SUBSTR).
TrapSUBSTR()() — skipping the failure case for SUBSTR.
ExSUBSTR()() → Dev walking through SUBSTR.

-- SUBSTR()() 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;

SUBSTR()()

SUBSTR()() — sample query

Short notes

Questions

SUBSTR()()

SUBSTR()() — sample query

Short notes

Questions