user: Question: How many different years was the name/designation CETME?
Columns: ['Name / designation', 'Year of introduction', 'Country of origin', 'Primary cartridge', 'primary user']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Armalite AR-10', '1957', 'United States', '7.62x51mm NATO', 'Portugal, Sudan']
SQL:

assistant: SELECT COUNT("Year of introduction") FROM "Table" WHERE "Name / designation" = 'CETME';