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.