Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE organizations (organization_id VARCHAR, parent_organization_id VARCHAR)
### Question:
Which organizations are not a parent organization of others? List the organization id.
### Answer:
SELECT organization_id FROM organizations EXCEPT SELECT parent_organization_id FROM organizations