mariadb-corporation REPLACE in MariaDB
Last updated: 2026-06-24
This skill covers REPLACE and its traps. REPLACE is a MariaDB extension (not standard SQL) that resolves a PRIMARY KEY/UNIQUE conflict by deleting the conflicting row(s) and inserting a new one. It is not an in-place update — that distinction is the source of nearly every REPLACE bug.
Default context: Assume MariaDB 11.8 LTS (GA May 2025) unless the user states another version. Anything available in current LTS branches (10.6, 10.11, 11.4, 11.8) is shown without a "since" annotation; only newer-than-10.6 features carry one.
What LLMs Often Miss
| If the agent writes / assumes… | …prefer the MariaDB form |
|---|---|
Uses REPLACE to mean "upsert / update if it exists" |
Use INSERT … ON DUPLICATE KEY UPDATE. REPLACE deletes the old row and inserts a new one — it does not update in place. The ON DUPLICATE KEY UPDATE form is what "upsert" almost always means. See mariadb-insert |
Assumes columns not listed in the REPLACE keep their old values (UPDATE-style) |
They are reset to their DEFAULT — because a brand-new row is inserted. A partial REPLACE silently wipes the columns you didn't mention. This is the most damaging REPLACE footgun |
Writes REPLACE … SET counter = counter + 1 expecting to read the old row |
The right-hand counter resolves to DEFAULT(counter), not the existing row's value — there is no "existing row" in a REPLACE. So this means DEFAULT(counter) + 1 |
Expects the replaced row to keep its AUTO_INCREMENT id |
A new AUTO_INCREMENT value is generated (old row deleted), burning ids and breaking any external references to the old id |
Assumes REPLACE only fires INSERT triggers and has no delete side effects |
It fires BEFORE DELETE → delete → AFTER DELETE → then INSERT triggers, and it activates ON DELETE foreign-key actions (e.g. ON DELETE CASCADE) on child tables — so a REPLACE can cascade-delete unrelated rows |
Thinks REPLACE matches on any column / the WHERE-like condition |
It acts only on PRIMARY KEY or UNIQUE index conflicts. With no such index, it's a plain INSERT. If a row conflicts on several unique keys, all matching rows are deleted before the insert |
Grants only INSERT to a user that runs REPLACE |
REPLACE needs both INSERT and DELETE privileges on the table — a direct consequence of the delete-then-insert mechanic |
Puts an aggregate or multi-row subquery in RETURNING |
RETURNING allows per-row expressions, stored functions, and single-row/single-column subqueries, but no aggregates and no multi-row subqueries. Use ROW_COUNT() for a count |
The upsert contrast (read this before using REPLACE)
-- REPLACE: deletes the existing row #1, inserts a fresh one.
-- → unlisted columns reset to DEFAULT, a new auto_increment id is burned,
-- ON DELETE cascades fire, DELETE+INSERT triggers fire.
REPLACE INTO t (id, name) VALUES (1, 'new');
-- ON DUPLICATE KEY UPDATE: keeps row #1, changes only `name`.
-- → other columns untouched, id preserved, no delete side effects.
INSERT INTO t (id, name) VALUES (1, 'new')
ON DUPLICATE KEY UPDATE name = VALUE(name);
Reach for REPLACE only when you genuinely want the row fully replaced (all columns reset, side effects intended). For "insert or update," ON DUPLICATE KEY UPDATE is correct.
Forms
All three forms accept [LOW_PRIORITY | DELAYED], an optional [INTO], an optional PARTITION (…), and an optional trailing RETURNING. There is no HIGH_PRIORITY for REPLACE, and DELAYED is legacy (a no-op on modern engines).
-- VALUES form:
REPLACE INTO t [PARTITION (p1)] (col, …) VALUES (expr | DEFAULT, …), (…)
[RETURNING select_expr [, …]];
-- SET form:
REPLACE INTO t SET col = {expr | DEFAULT}, … [RETURNING …];
-- SELECT form (can copy across databases via db.tbl; source ≠ target):
REPLACE INTO t (col, …) SELECT … [RETURNING …];
REPLACE cannot be combined with ON DUPLICATE KEY UPDATE (they're mutually exclusive duplicate-handling strategies).
RETURNING
REPLACE INTO t (id, name) VALUES (1, 'new')
RETURNING id, name, UPPER(name) AS uc;
Returns the newly inserted rows. Expressions, virtual columns, AS aliases, stored functions, single-value subqueries, and prepared statements are supported; aggregates and multi-row subqueries are not.
See Also
mariadb-insert—INSERT … ON DUPLICATE KEY UPDATE(the upsert you usually want),INSERT IGNORE, and the sharedRETURNING/PARTITION/priority surfacemariadb-create-table—AUTO_INCREMENT,DEFAULTexpressions, and thePRIMARY KEY/UNIQUEindexes that determine whenREPLACEfires and which columns reset- Canonical references on
mariadb.com/docs(consult only for edge cases not covered here):
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