Function GetColumnDefCollation

src/backend/parser/parse_type.c:539–573

* GetColumnDefCollation * * Get the collation to be used for a column being defined, given the * ColumnDef node and the previously-determined column type OID. * * pstate is only used for error location purposes, and can be NULL. */

 * pstate is only used for error location purposes, and can be NULL.
 */
Oid
GetColumnDefCollation(ParseState *pstate, ColumnDef *coldef, Oid typeOid)
{
	Oid			result;
	Oid			typcollation = get_typcollation(typeOid);
	int			location = coldef->location;

	if (coldef->collClause)
	{
		/* We have a raw COLLATE clause, so look up the collation */
		location = coldef->collClause->location;
		result = LookupCollation(pstate, coldef->collClause->collname,
								 location);
	}
	else if (OidIsValid(coldef->collOid))
	{
		/* Precooked collation spec, use that */
		result = coldef->collOid;
	}
	else
	{
		/* Use the type's default collation if any */
		result = typcollation;
	}

	/* Complain if COLLATE is applied to an uncollatable type */
	if (OidIsValid(result) && !OidIsValid(typcollation))
		ereport(ERROR,
				(errcode(ERRCODE_DATATYPE_MISMATCH),
				 errmsg("collations are not supported by type %s",
						format_type_be(typeOid)),
				 parser_errposition(pstate, location)));

	return result;
}

/* return a Type structure, given a type id */
/* NB: caller must ReleaseSysCache the type tuple when done with it */