With a table such as:
{| class="wikitable sortable" ! Name || Date || Number |- | A || 1967-01-01 || 1967 |- | B || 1985-01-01 || 1985 |- | C || 2001-01-01 || 2001 |- | D || 1825-01-01 || 1825 |- | E || || |}
When sorting on the date column, the blank values are placed in the middle of the table rather than at one of the ends.