user: Question: What is the exit date of the player who transferred to Portsmouth?
Columns: ['Exit date', 'Pos.', 'Player', 'To club', 'Transfer fee']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['15 May 2007', 'DF', 'Hatem Trabelsi', 'Al-Hilal', 'Released']
SQL:

assistant: SELECT "Exit date" FROM "Table" WHERE "To club" = 'Portsmouth';