user: Question: How many people were first elected with an incument of Diane Watson?
Columns: ['District', 'Incumbent', 'Party', 'First elected', 'Results', 'Candidates']
Types: ['text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['California 7', 'George Miller', 'Democratic', 1974.0, 'Re-elected', 'George Miller (D) 83.9% Camden McConnell (L) 16.1%']
SQL:

assistant: SELECT COUNT("First elected") FROM "Table" WHERE "Incumbent" = 'Diane Watson';