user: Question: What is the average rating of viewers 18 to 49 where the total viewer count is 3.93 million and share less than 4?
Columns: ['Episode', 'Air Date', 'Timeslot (EST)', 'Season', 'Rating', 'Share', '18–49', 'Viewers (m)', 'Rank (#)']
Types: ['text', 'text', 'text', 'real', 'real', 'real', 'real', 'real', 'text']
Sample row: ['" I Knew You When "', 'October 1, 2008', 'Fri. 9:00PM', 2009.0, 2.8, 5.0, 1.6, 4.54, 'N/A']
SQL:

assistant: SELECT AVG("18–49") FROM "Table" WHERE "Viewers (m)" = 3.93 AND "Share" < 4.0;