Show ids for all documents.
select document_id from documents_with_expenses
Also show their budget type descriptions.
select t1.document_id, t2.budget_type_description from documents_with_expenses as t1 join ref_budget_codes as t2 on t1.budget_type_code = t2.budget_type_code
Show ids for those documents with budget types described as 'Government'.
select t1.document_id from documents_with_expenses as t1 join ref_budget_codes as t2 on t1.budget_type_code = t2.budget_type_code where t2.budget_type_description = "Government"