user: Question: What is the semi-final dual television commentator status of the year with Pierre Tchernia as the grand final television commentator and an Unknown spokesperson?
Columns: ['Year(s)', 'Grand Final Television Commentator', 'Grand Final Dual Television Commentator', 'Spokesperson', 'Semi Final Television Commentator', 'Semi Final Dual Television Commentator']
Types: ['real', 'text', 'text', 'text', 'text', 'text']
Sample row: [1956.0, 'Michèle Rebel', 'No Dual Television Commentator', 'No Spokesperson', 'No Semi Finals', 'No Semi Finals']
SQL:

assistant: SELECT "Semi Final Dual Television Commentator" FROM "Table" WHERE "Grand Final Television Commentator" = 'Pierre Tchernia' AND "Spokesperson" = 'Unknown';