user: Question: When Ihaia Tainui is the incumbent what is the date?
Columns: ['By-election', 'Electorate', 'Date', 'Incumbent', 'Reason', 'Winner']
Types: ['real', 'text', 'text', 'text', 'text', 'text']
Sample row: [1880.0, 'Rangitikei', '8 May', 'William Jarvis Willis', 'Resignation', 'William Fox']
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "Incumbent" = 'Ihaia Tainui';