user: Question: What is the Date of vacancy for Tommy McLean?
Columns: ['Team', 'Outgoing manager', 'Manner of departure', 'Date of vacancy', 'Replaced by', 'Date of appointment']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Dundee United', 'Tommy McLean', 'Mutual consent', '4 September 1997', 'Paul Sturrock', '5 September 1997']
SQL:

assistant: SELECT "Date of vacancy" FROM "Table" WHERE "Outgoing manager" = 'Tommy McLean';