SQL · Theory

Not Exists

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Not Exists

Ananya only reaches for Not Exists when Not Exists on Ananya's board has to stay correct in lab hour.

For Not Exists, InnoDB is in play. Don’t blame it until you have traced Not Exists on Ananya's board.

Without Not Exists, lab hour gets messy and Not Exists on Ananya's board is hard to trust.

Not Exists shows up in lab hour. Name Not Exists on Ananya's board, not “a real-world scenario”.

If Not Exists on Ananya's board breaks under Not Exists, check copy-pasting Not Exists without a dry-run first.

Not Exists is not a lonely heading. Ananya ties it to Not Exists on Ananya's board.

Close Not Exists with: “If I skip it, Not Exists on Ananya's board goes wrong like this: copy-pasting Not Exists without a dry-run.”

Exam tip

For Not Exists: definition + lab hour + one failure.

Not Exists — sample query

CREATE TABLE a (id INTEGER, label TEXT);
CREATE TABLE b (id INTEGER, label TEXT);
INSERT INTO a VALUES (1, 'x'), (2, 'y');
INSERT INTO b VALUES (2, 'y'), (3, 'z');
SELECT label FROM a
UNION
SELECT label FROM b;

Not Exists — uNION merges result sets and drops duplicate rows.

Short notes

DefNot Exists — Ananya uses it for Not Exists on Ananya's board in lab hour.
RuleNot Exists → one Not Exists step Ananya can write from memory.
RememberNot Exists + InnoDB (lab hour).
UseNot Exists in lab hour (Not Exists on Ananya's board).
TrapNot Exists — copy-pasting Not Exists without a dry-run.
ExNot Exists → Not Exists on Ananya's board.

CREATE TABLE a (id INTEGER, label TEXT); CREATE TABLE b (id INTEGER, label TEXT); INSERT INTO a VALUES (1, 'x'), (2, 'y'); INSERT INTO b VALUES (2, 'y'), (3, 'z'); SELECT label FROM a UNION SELECT label FROM b;

Not Exists

Not Exists — sample query

Short notes

Questions

Not Exists

Not Exists — sample query

Short notes

Questions