All errors › ORA errors
ORA-01427: Single-row subquery returns more than one row
What it means
A subquery used with =, <, > or in the SELECT list returned more than one row.
How to fix it
Use IN / EXISTS instead of =, add the missing join condition to the subquery, or aggregate it. Find the duplicates with GROUP BY ... HAVING COUNT(*) > 1.
Catch it before it runs
ORA Error Helper
Explains ORA-/PLS- codes inside JetBrains IDEs and DataGrip. PL/SQL Lint
Flags risky PL/SQL patterns while you type. Oracle Plan Reader
Reads execution plans and points at the slow step. PL/SQL in Practice
Kindle book with practical PL/SQL for working developers.
Explains ORA-/PLS- codes inside JetBrains IDEs and DataGrip. PL/SQL Lint
Flags risky PL/SQL patterns while you type. Oracle Plan Reader
Reads execution plans and points at the slow step. PL/SQL in Practice
Kindle book with practical PL/SQL for working developers.
Nearby errors
Updated 2026-11-12.