1400
MariaDBerrorqueryhigh confidence
Subquery returns more than 1 row
Production Risk
Low — query fails; no data changed.
What this means
A scalar subquery used in a SELECT list, WHERE clause, or SET returned more than one row.
Why it happens
- 1SELECT (SELECT col FROM t) — table has multiple rows
- 2Scalar subquery in SET clause matches multiple rows
How to reproduce
trigger — this will error
trigger — this will error
SELECT (SELECT name FROM users WHERE active = 1);
expected output
ERROR 1400 (21000): Subquery returns more than 1 row
Fix 1
Add LIMIT 1
Add LIMIT 1
SELECT (SELECT name FROM users WHERE active = 1 LIMIT 1);
Why this works
Forces at most one row from the subquery.
Fix 2
Use an aggregate
Use an aggregate
SELECT (SELECT MAX(name) FROM users WHERE active = 1);
Why this works
Returns a single scalar value.
What not to do
✕
Sources
Official documentation ↗
MySQL 8.0 — 1242 / 1400 ER_SUBQUERY_NO_1_ROW
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