Upsert generator

Upsert into MySQL: INSERT … ON DUPLICATE KEY UPDATE

Name your table, key and columns and get the statement MySQL actually accepts, with a guard so an older row never overwrites a newer one. Below it: how the mechanic works, what breaks, and how Datrise loads MySQL incrementally.

Generate the statement

Statement · INSERT … ON DUPLICATE KEY UPDATE

INSERT INTO `deals` (`id`, `name`, `stage`, `amount`, `owner_id`, `updated_at`)
SELECT s.`id`, s.`name`, s.`stage`, s.`amount`, s.`owner_id`, s.`updated_at`
FROM `deals_staging` AS s
ON DUPLICATE KEY UPDATE
  `name` = IF(`deals`.`updated_at` < s.`updated_at`, s.`name`, `deals`.`name`),
  `stage` = IF(`deals`.`updated_at` < s.`updated_at`, s.`stage`, `deals`.`stage`),
  `amount` = IF(`deals`.`updated_at` < s.`updated_at`, s.`amount`, `deals`.`amount`),
  `owner_id` = IF(`deals`.`updated_at` < s.`updated_at`, s.`owner_id`, `deals`.`owner_id`),
  `updated_at` = IF(`deals`.`updated_at` < s.`updated_at`, s.`updated_at`, `deals`.`updated_at`);

How the upsert works in MySQL

MySQL's upsert is INSERT … ON DUPLICATE KEY UPDATE. It triggers on any PRIMARY KEY or UNIQUE index violation, and the UPDATE branch can reference the row that failed to insert. The generated form selects from a staging table aliased as s and updates each column from s, wrapped in IF() so a row with an older updated-at leaves the stored values alone.

Two things trip people up. Affected-rows counts 1 for an insert, 2 for an update and 0 for a no-op, which matters when a driver uses it to report success. And InnoDB reserves an auto-increment value for every attempted insert, so a table upserted daily shows gaps in surrogate ids; that is expected, not a lost row. Use utf8mb4 on the target so CRM text with emoji survives the write.

Before you run it

"Duplicate" means any PRIMARY KEY or UNIQUE index, not just the one you think of as the business key. A second unique index on email will silently merge rows you meant to keep apart.
The IF() guard keeps the existing row when the incoming updated-at is older. Without it the last write wins, whatever its timestamp.
Avoid REPLACE INTO for upserts: it deletes and re-inserts, which fires DELETE triggers, cascades foreign keys and burns auto-increment values.

Questions people ask

Why does ON DUPLICATE KEY UPDATE merge rows I did not expect?

It fires on every unique index, not only the primary key. A unique index on email will fold two contacts with the same address into one. Drop or relax secondary unique indexes on synced tables.

REPLACE INTO or ON DUPLICATE KEY UPDATE?

ON DUPLICATE KEY UPDATE. REPLACE deletes the old row and inserts a new one, which fires DELETE triggers, cascades foreign keys and changes the auto-increment id.

Is VALUES(col) still valid?

It works but is deprecated since MySQL 8.0.20. Referencing the staging alias (s.col) as generated, or the INSERT … AS new alias form, is the supported syntax.

The same generator for other destinations

Skip writing the merge at all

Datrise lands CRM and SaaS entities into MySQL with this exact mechanic, a watermark on updated-at, and typed columns, so the statement above is what runs on your behalf. Join the waitlist to get early access.

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