SQL · Theory

UPSERT

Theory

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UPSERT

Upsert = insert or update if the key exists. MySQL: INSERT … ON DUPLICATE KEY UPDATE … or REPLACE (harsher). Example: refresh Asha’s marks if roll 12 exists, else insert.

Needs a PRIMARY/UNIQUE key to detect ‘exists’.

Trap — upsert without a unique key — always inserts.

On the example next to this theory: UPSERT: create two demo rows, then SELECT qty >= 2 ordered. Say which labels come back.

Exam tip

INSERT … ON DUPLICATE KEY UPDATE marks = 90;

UPSERT — sample query

-- UPSERT
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;

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

Short notes

DefUpsert = INSERT or UPDATE on key clash.
RuleNeed PK/UNIQUE. Prefer ON DUPLICATE KEY UPDATE.
TrapNo unique key.

-- UPSERT 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;

UPSERT

UPSERT — sample query

Short notes

Questions

UPSERT

UPSERT — sample query

Short notes

Questions