Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.

### Instruction:

Convert text to sql: What document status codes do we have? | ref_document_types : document_type_code , document_type_description | roles : role_code , role_description | addresses : address_id , address_details | ref_document_status : document_status_code , document_status_description | ref_shipping_agents : shipping_agent_code , shipping_agent_name , shipping_agent_description | documents : document_id , document_status_code , document_type_code , shipping_agent_code , receipt_date , receipt_number , other_details | employees : employee_id , role_code , employee_name , other_details | document_drafts : document_id , draft_number , draft_details | draft_copies : document_id , draft_number , copy_number | circulation_history : document_id , draft_number , copy_number , employee_id | documents_mailed : document_id , mailed_to_address_id , mailing_date | documents.shipping_agent_code = ref_shipping_agents.shipping_agent_code | documents.document_status_code = ref_document_status.document_status_code | documents.document_type_code = ref_document_types.document_type_code | employees.role_code = roles.role_code | document_drafts.document_id = documents.document_id | draft_copies.document_id = document_drafts.document_id | draft_copies.draft_number = document_drafts.draft_number | circulation_history.employee_id = employees.employee_id | circulation_history.document_id = draft_copies.document_id | circulation_history.draft_number = draft_copies.draft_number | circulation_history.copy_number = draft_copies.copy_number | documents_mailed.mailed_to_address_id = addresses.address_id | documents_mailed.document_id = documents.document_id | 

### Response:

select _ from _ | select document_status_code from ref_document_status