unnest() — PostgreSQL array function

unnest(): expand array to set of rows. PostgreSQL array functions — signature, volatility, version applicability and an illustrative example.

The Sev-1 Admin
The Sev-1 Admin  ·  2 min read

Summary

unnest is a PostgreSQL built-in function in the Array Functions group. PostgreSQL’s system catalog (pg_proc) describes it as: “expand array to set of rows”.

Signature

unnest has 2 documented overloaded forms:

unnest(anyarray) → setof anyelement
unnest(anymultirange) → setof anyrange

Argument and return types are taken from the pg_proc catalog; internal type names are shown using their readable SQL spellings (for example int4 is shown as integer). (Derived from the catalog — see the linked reference for the canonical documentation.)

Classification

  • Category: Array Functions
  • Kind: Function
  • Volatility: IMMUTABLE — Marked IMMUTABLE — it always returns the same result for the same arguments and can be used in indexes and other contexts that require immutability.
  • Returns: anyelement, anyrange (set-returning)

Example

Illustrative form (replace placeholder values with your own data):

SELECT * FROM unnest(ARRAY[1,2,3]);

The example above is illustrative and is meant to show calling syntax only; consult the linked PostgreSQL documentation for exact semantics, edge cases and accepted argument combinations.

Version applicability

unnest is present across the surveyed releases (PostgreSQL 15, 16, 17, 18, 19). On older major versions, behaviour may differ in detail — always check the documentation for the version you run.

Related & references

Reference: PostgreSQL documentation — Array Functions.