user: Question: What is the commissioned for Vietnam?
Columns: ['Operator', 'Shipyard', 'Project', 'Commissioned', 'Status']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ["People's Republic of China", 'Saint Petersburg', '636', '26 August 1997', 'active as of 2006']
SQL:

assistant: SELECT "Commissioned" FROM "Table" WHERE "Operator" = 'Vietnam';