user: Question: Name the period with matches of 0 0 of Portugal
Columns: ['Country', 'Player name', 'Period', 'Position', 'Matches', 'Goals']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Albania', 'Elton Çeno', '1998–1999', 'Midfielder', '0 5', '0 0']
SQL:

assistant: SELECT "Period" FROM "Table" WHERE "Matches" = '0 0' AND "Country" = 'Portugal';