user: Question: What is Left Office, when Party is Vacant (1999-2001)?
Columns: ['Name', 'Took Office', 'Left Office', 'President', 'Party']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Sisavath Keobounphanh', '1996', '1998', 'Nouhak Phoumsavanh', "Lao People's Revolutionary Party"]
SQL:

assistant: SELECT "Left Office" FROM "Table" WHERE "Party" = 'Vacant (1999-2001)';