Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE organizations (organization_id VARCHAR, parent_organization_id VARCHAR)

### Question ###
Which organizations are not a parent organization of others? List the organization id.

### Accurate SQL ###

SELECT organization_id FROM organizations EXCEPT SELECT parent_organization_id FROM organizations