user: Question: On how many different dates was the episode written by Charlie Day aired for the first time?
Columns: ['No. in series', 'No. in season', 'Title', 'Directed by', 'Written by', 'Original air date', 'Production code']
Types: ['real', 'real', 'text', 'text', 'text', 'text', 'text']
Sample row: [10.0, 3.0, '" Dennis and Dee Go on Welfare "', 'Dan Attias', 'Rob McElhenney', 'July6,2006', 'IP02004']
SQL:

assistant: SELECT COUNT("Original air date") FROM "Table" WHERE "Written by" = 'Charlie Day';