Function LookupExplicitNamespace

src/backend/catalog/namespace.c:2969–3000

* LookupExplicitNamespace * Process an explicitly-specified schema name: look up the schema * and verify we have USAGE (lookup) rights in it. * * Returns the namespace OID */

 * Returns the namespace OID
 */
Oid
LookupExplicitNamespace(const char *nspname, bool missing_ok)
{
	Oid			namespaceId;
	AclResult	aclresult;

	/* check for pg_temp alias */
	if (strcmp(nspname, "pg_temp") == 0)
	{
		if (TempNamespaceValid(true))
			return myTempNamespace;

		/*
		 * Since this is used only for looking up existing objects, there is
		 * no point in trying to initialize the temp namespace here; and doing
		 * so might create problems for some callers --- just fall through.
		 */
	}

	namespaceId = get_namespace_oid(nspname, missing_ok);
	if (missing_ok && !OidIsValid(namespaceId))
		return InvalidOid;

	aclresult = pg_namespace_aclcheck(namespaceId, GetUserId(), ACL_USAGE);
	if (aclresult != ACLCHECK_OK)
		aclcheck_error(aclresult, OBJECT_SCHEMA,
					   nspname);
	/* Schema search hook for this lookup */
	InvokeNamespaceSearchHook(namespaceId, true);

	return namespaceId;
}

/*
 * LookupCreationNamespace