user: Question: What is the date of vacancy for the Liverpool team with a table named Pre-season?
Columns: ['Team', 'Outgoing manager', 'Manner of departure', 'Date of vacancy', 'Table', 'Incoming manager', 'Date of appointment']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['West Ham United', 'Gianfranco Zola', 'Contract terminated', '11 May 2010', 'Pre-season', 'Avram Grant', '3 June 2010']
SQL:

assistant: SELECT "Date of vacancy" FROM "Table" WHERE "Table" = 'Pre-season' AND "Team" = 'Liverpool';