# 428C9 — Generated-always column assignment > PostgreSQL SQLSTATE 428C9: Generated-always column assignment (generated_always), source-backed diagnosis and recovery guidance. --- # 428C9 — Generated-always column assignment ## At a glance {#at-a-glance} `428C9` (**generated_always**) is a rewrite-stage `ERROR` when an INSERT or UPDATE supplies a value where PostgreSQL must generate it or receive `DEFAULT`. Identity columns and generated columns follow different assignment rules, so the operation and column metadata matter. | Field | Value | | --- | --- | | SQLSTATE | `428C9` | | Condition | `generated_always` | | Status | `active` | | Known present by | `10.0` | | Locked snapshots | `10.23, 11.22, 12.22, 13.23, 14.24, 15.19, 16.15, 17.11, 18.6, 19beta3` | | Macros | `ERRCODE_GENERATED_ALWAYS` | | Aliases | `—` | ## Meaning {#meaning} The rewriter computes `apply_default` for an omitted INSERT target or an explicit `DEFAULT`. For an identity column marked `GENERATED ALWAYS`, a non-default INSERT is rejected unless `OVERRIDING SYSTEM VALUE` is present; `OVERRIDING USER VALUE` instead forces the default. An identity column marked `BY DEFAULT` accepts a supplied value, but `OVERRIDING USER VALUE` still forces generation. Generated columns take only `DEFAULT`, regardless of an `OVERRIDING` clause. The INSERT branches identify the column in DETAIL, and the identity-always branch adds HINT `Use OVERRIDING SYSTEM VALUE to override.` For UPDATE, the guard covers identity `GENERATED ALWAYS` and every generated column when a non-default target entry is present; UPDATE has no `OVERRIDING` escape. After the guard, a virtual generated column gets a null target entry and a stored generated column is filled by the executor. This storage behavior is part of the 18.6 source path and does not turn the catalogue's 10.0 SQLSTATE lower bound into a claim that every generated-column feature existed in 10.0. ## Diagnosis {#diagnosis} Inspect `pg_attribute.attidentity` (`a` for `ALWAYS`, `d` for `BY DEFAULT`) and `attgenerated` (`s` for stored, `v` for virtual), then record whether the command is INSERT or UPDATE and whether the target entry is omitted, `DEFAULT`, or a value. For an INSERT from `VALUES`, confirm whether the offending row item is actually `DEFAULT`; the rewriter has a separate all-default check. Read the primary, DETAIL, and HINT together: identity-always and generated-column INSERTs share a primary template but have different DETAIL/HINT contracts. ## Response {#response} For identity `GENERATED ALWAYS`, omit the value, use `DEFAULT`, or use `OVERRIDING SYSTEM VALUE` only when the application deliberately owns the identity value. For identity `BY DEFAULT`, leave the value in place when that is the contract; use `OVERRIDING USER VALUE` when the server must generate it. Remove assignments to generated columns and do not try to bypass the guard with a cast. If the `ERROR` occurred inside an explicit transaction, roll back to a suitable savepoint or roll back the transaction before issuing the corrected statement; this page has no runtime observation of that recovery. ## Messages {#messages} The selected 18.6 groups are explicit `ERROR`s: | Operation | Primary | DETAIL | HINT | | --- | --- | --- | --- | | identity `GENERATED ALWAYS` INSERT | `cannot insert a non-DEFAULT value into column "%s"` | `Column "%s" is an identity column defined as GENERATED ALWAYS.` | `Use OVERRIDING SYSTEM VALUE to override.` | | generated-column INSERT | `cannot insert a non-DEFAULT value into column "%s"` | `Column "%s" is a generated column.` | none | | identity `GENERATED ALWAYS` UPDATE | `column "%s" can only be updated to DEFAULT` | `Column "%s" is an identity column defined as GENERATED ALWAYS.` | none | | generated-column UPDATE | `column "%s" can only be updated to DEFAULT` | `Column "%s" is a generated column.` | none | The fixed source also distinguishes virtual generated storage (null target entry) from stored generated storage (executor fill). Each `%s` is dynamic; no concrete placeholder value or runtime result is claimed. ## Versions {#versions} The catalogue records the condition by 10.0 and locks snapshots through 18.6 and 19beta3. That is a definition lower bound, not a claim that identity, stored-generated, and virtual-generated features all share that introduction point. The selected mechanism is PostgreSQL 18.6 source; runtime was not run. ## Related {#related} - [`42804`](../42804/) - [`42601`](../42601/) - [`23502`](../23502/) ## Sources {#sources} - `src.errcodes.428C9.18.6` — `src/backend/utils/errcodes.txt` line 355, fixed at `724edf9bde9d356724ad384a2e196edc3c9f80f7`; SHA-256 `6e8de346643ba84aa3c9c6a73360acfc7b2dfb89162c06c08ce9bf5bcd5bbcba` ([source](https://github.com/postgres/postgres/blob/724edf9bde9d356724ad384a2e196edc3c9f80f7/src/backend/utils/errcodes.txt#L355)). - `src.call.428C9.353c4cc772b5ae9adad09c67` — `src/backend/rewrite/rewriteHandler.c` lines 942-948, fixed at `724edf9bde9d356724ad384a2e196edc3c9f80f7`; SHA-256 `5a34bf31f424abbf46cd926da1fefcd9360c4d527a87d8a0ac9f653d67c2206a` ([source](https://github.com/postgres/postgres/blob/724edf9bde9d356724ad384a2e196edc3c9f80f7/src/backend/rewrite/rewriteHandler.c#L942-L948)). - `src.call.428C9.47aaa60ecb1566d462ffaa86` — `src/backend/rewrite/rewriteHandler.c` lines 981-986, fixed at `724edf9bde9d356724ad384a2e196edc3c9f80f7`; SHA-256 `5a34bf31f424abbf46cd926da1fefcd9360c4d527a87d8a0ac9f653d67c2206a` ([source](https://github.com/postgres/postgres/blob/724edf9bde9d356724ad384a2e196edc3c9f80f7/src/backend/rewrite/rewriteHandler.c#L981-L986)). - `src.call.428C9.8585d423db2446a6222cbf57` — `src/backend/rewrite/rewriteHandler.c` lines 1008-1013, fixed at `724edf9bde9d356724ad384a2e196edc3c9f80f7`; SHA-256 `5a34bf31f424abbf46cd926da1fefcd9360c4d527a87d8a0ac9f653d67c2206a` ([source](https://github.com/postgres/postgres/blob/724edf9bde9d356724ad384a2e196edc3c9f80f7/src/backend/rewrite/rewriteHandler.c#L1008-L1013)). - `src.call.428C9.generated-update` — `src/backend/rewrite/rewriteHandler.c` lines 1015-1030, fixed at `724edf9bde9d356724ad384a2e196edc3c9f80f7`; SHA-256 `5a34bf31f424abbf46cd926da1fefcd9360c4d527a87d8a0ac9f653d67c2206a` ([source](https://github.com/postgres/postgres/blob/724edf9bde9d356724ad384a2e196edc3c9f80f7/src/backend/rewrite/rewriteHandler.c#L1015-L1030)). - `src.calls.REL_18_6.428C9` — resolved core call groups; SHA-256 `9ee8a0e81d8f0825c5c1ae45583439859a26e602bdd4ce2f2a62aa278867ccbf`. - [`authored evidence`](../data/evidence/428c9.json) — source claims, message roles, and runtime boundary.