# Common codes > A curated list of SQLSTATE values useful during incident triage. --- This is an editorial entry point for frequent diagnosis paths. It is not a measured ranking of production frequency; each row states the practical question the entry helps answer and preserves its review state. | Code | Condition | Why start here | | --- | --- | --- | | [`23505`](../23505/) | `unique_violation` | Duplicate keys, constraints, and idempotent writes. | | [`23503`](../23503/) | `foreign_key_violation` | Foreign-key repair and dependency order. | | [`23502`](../23502/) | `not_null_violation` | Missing required values and input validation. | | [`23514`](../23514/) | `check_violation` | CHECK constraints and invariant failures. | | [`23P01`](../23p01/) | `exclusion_violation` | Exclusion constraints and range conflicts. | | [`40P01`](../40p01/) | `deadlock_detected` | Deadlock diagnosis, rollback, and lock ordering. | | [`40001`](../40001/) | `serialization_failure` | Serializable retry and fresh transaction snapshots. | | [`25P02`](../25p02/) | `in_failed_sql_transaction` | The failed transaction state that follows an error. | | [`42P01`](../42p01/) | `undefined_table` | Missing relations and search-path diagnosis. | | [`42601`](../42601/) | `syntax_error` | Syntax errors before a statement can execute. | | [`42501`](../42501/) | `insufficient_privilege` | Privilege checks and authorization failures. | | [`28P01`](../28p01/) | `invalid_password` | Password authentication and connection setup. | | [`57014`](../57014/) | `query_canceled` | Cancellation, statement_timeout, and safe follow-up. | | [`53300`](../53300/) | `too_many_connections` | Connection limits and admission failures. | | [`2202E`](../2202e/) | `array_subscript_error` | Array dimensions, concatenation, and type rules. | | [`01000`](../01000/) | `warning` | Warning dispatch and non-error diagnostics. | | [`P0001`](../p0001/) | `raise_exception` | Application-defined PL/pgSQL exceptions. | | [`XX000`](../xx000/) | `internal_error` | Internal-error safety boundaries and escalation. | --- Backlinks: - [SQLSTATE Atlas](/)