CREATE TABLE table_4142 ("By-election" FLOAT, "Electorate" TEXT, "Date" TEXT, "Incumbent" TEXT, "Reason" TEXT, "Winner" TEXT)

When ihaia tainui is the incumbent what is the date?
SELECT "Date" FROM table_4142 WHERE "Incumbent" = 'Ihaia Tainui'
SELECT "Date" FROM "table_4142" WHERE "Incumbent" = 'Ihaia Tainui'