CREATE TABLE table_35478 ("Exit date" TEXT, "Pos." TEXT, "Player" TEXT, "To club" TEXT, "Transfer fee" TEXT)

What is the exit date of the player who transferred to Portsmouth?
SELECT "Exit date" FROM table_35478 WHERE "To club" = 'portsmouth'
SELECT "Exit date" FROM "table_35478" WHERE "To club" = 'portsmouth'