My second external query

Syntax

{{#ask:
 [[Category:SMWCon]]
 |?Has planned start#-F[Y-m-d]=start date|+align=center
 |?Has planned finish#-F[Y-m-d]=end date|+align=center
 |source=smwo
 |mainlabel=conference
 |headers=plain
 |sort=Has planned start
 |order=descending
}}

Result