user: Question: On what Date did the massacre result with 21 Injured?
Columns: ['Perpetrator', 'Date', 'Year', 'Location', 'Country', 'Killed', 'Injured', 'Additional Notes']
Types: ['text', 'text', 'real', 'text', 'text', 'real', 'text', 'text']
Sample row: ['Kehoe, Andrew Philip , 55', '05.18 May 18', 1927.0, 'Bath Township , MI', 'U.S.', 44.0, '58', 'Committed suicide']
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "Injured" = '21';