# 42702 — ambiguous_column

> PostgreSQL SQLSTATE 42702: ambiguous_column, source-backed diagnosis and recovery guidance.
---

# 42702

## At a glance {#at-a-glance}

SQLSTATE `42702` is **ambiguous_column** in Class `42`. `42702` is ambiguous_column. The selected join exposes `id` from two real tables and an unqualified `SELECT id` reports `column reference "%s" is ambiguous`.

<!-- BEGIN SQLSTATE FACTS: generated by scripts/generate.py; do not edit -->

| Field | Value |
| --- | --- |
| SQLSTATE | `42702` |
| Condition | `ambiguous_column` |
| Status | `active` |
| Known present by | `7.4` |
| Locked snapshots | `9.0.23, 9.1.24, 9.2.24, 9.3.25, 9.4.26, 9.5.25, 9.6.24, 10.23, 11.22, 12.22, 13.23, 14.24, 15.19, 16.15, 17.11, 18.6, 19beta3` |
| Macros | `ERRCODE_AMBIGUOUS_COLUMN` |
| Aliases | `—` |

<!-- source facts: data/errcodes/42702.json -->
<!-- END SQLSTATE FACTS -->

## Meaning {#meaning}

`42702` is ambiguous_column. In `colNameToVar`, PostgreSQL scans the visible namespace for an unqualified name. Once two visible range-table entries produce a match in the same lookup, the parser raises `ERROR` `column reference "%s" is ambiguous`; the selected join exposes `id` from both real tables. The branch is about name resolution, before execution or row values can disambiguate it.

## Diagnosis {#diagnosis}

Inspect aliases, CTEs, join inputs, lateral visibility, and every relation contributing the name in the current query scope. An unqualified name can be ambiguous even when the two columns contain the same value; PostgreSQL must resolve the source before executing the query. This is parse-time name resolution, so the selected autocommit session remains `IDLE`; it is distinct from 42703 where no matching column exists. An explicit transaction still follows the usual statement-ERROR transaction-state rule.

## Response {#response}

Qualify the intended column with a stable table alias (or remove the unintended relation from the scope), then verify the returned row. Do not solve the ambiguity by relying on join order or equal values. If generated SQL introduces aliases or CTEs, make the qualification part of the query-builder contract and test the selected source column.

## Messages {#messages}

The selected `parse_relation.c` branch emits an explicit `ERROR` with primary `column reference "%s" is ambiguous`; `%s` is the unresolved column name and parser position is contextual. A client exception without the server SQLSTATE and primary is not sufficient to claim `42702`.

## Representative case {#case}

<!-- BEGIN SQLSTATE SNIPPET: ambiguous_column -->

The page uses the same statements as the runner registry. Generated names such as `syntax_schema` and `syntax_role` are replaced by disposable runner values when executed.

```sql
CREATE TABLE syntax_schema.left_table (id integer);
CREATE TABLE syntax_schema.right_table (id integer);
INSERT INTO syntax_schema.left_table VALUES (1);
INSERT INTO syntax_schema.right_table VALUES (1);
SELECT id FROM syntax_schema.left_table, syntax_schema.right_table;
SELECT syntax_schema.left_table.id FROM syntax_schema.left_table, syntax_schema.right_table;
```

<!-- END SQLSTATE SNIPPET -->

The selected 18.6 run reports the structured diagnostic and passes the repair assertions; the 10.21 run passes the same case-specific checks. The downloadable case and evidence projections are [`42702 case JSON`](../data/cases/42702.json) and [`authored evidence`](../data/evidence/42702.json). The runner manifest is `verify/cases/42702/cases.json`, and the page SQL is checked against its shared registry.

## Versions {#versions}

The selected natural runtime scope is PostgreSQL 18.6 and 10.21; it does not infer behavior for every intermediate release.

## Related {#related}

- [`42703` — undefined_column](../42703/)
- [`42601` — syntax_error](../42601/)

## Sources {#sources}

- `src.errcodes.18.6` — fixed `errcodes.txt` definition at commit `724edf9bde9d356724ad384a2e196edc3c9f80f7`; SHA-256 `6e8de346643ba84aa3c9c6a73360acfc7b2dfb89162c06c08ce9bf5bcd5bbcba` ([source](https://github.com/postgres/postgres/blob/724edf9bde9d356724ad384a2e196edc3c9f80f7/src/backend/utils/errcodes.txt)).
- `src.ambiguous-column.18.6` — `src/backend/parser/parse_relation.c` at `REL_18_6` commit `724edf9bde9d356724ad384a2e196edc3c9f80f7`; fixed blob SHA-256 `0d9c88f4a8def4c2d982c33f13208590e21ecf5e6f8cd9d7faa223dc771c9a9a` ([source](https://github.com/postgres/postgres/blob/724edf9bde9d356724ad384a2e196edc3c9f80f7/src/backend/parser/parse_relation.c#L960-L964)).
- `src.ambiguous-column.10.23` — `src/backend/parser/parse_relation.c` at `REL_10_23` commit `02991e79f8f58bc208f05dcc8af0c62dbe0a6ea4`; fixed blob SHA-256 `a34f40fc93fa5df0015fe5af5ee7761ccba2d16a791cda69ae07848ed27616b5` ([source](https://github.com/postgres/postgres/blob/02991e79f8f58bc208f05dcc8af0c62dbe0a6ea4/src/backend/parser/parse_relation.c#L787-L791)).
- `src.calls.REL_18_6` / `src.calls.REL_10_23` — fixed call scans, SHA-256 `9ee8a0e81d8f0825c5c1ae45583439859a26e602bdd4ce2f2a62aa278867ccbf` / `00d16d3eb01b71ccf1b245c8f3102f9d0ec9f36fb02777b8dd1b99fcb263040c`.