user: Question: What is the minimum first elected for Ed Markey?
Columns: ['District', 'Incumbent', 'Party', 'First elected', 'Result', 'Candidates']
Types: ['text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['Massachusetts 1', 'Silvio Conte', 'Republican', 1958.0, 'Re-elected', 'Silvio Conte (R) 72.9% Mary L. Wentworth (D) 27.1%']
SQL:

assistant: SELECT MIN("First elected") FROM "Table" WHERE "Incumbent" = 'Ed Markey';