The standard date/time field extract function is supported for Hour, generating EXTRACT(HOUR FROM date/time expression). If this function is applied to a column or expression of type other than Time or Timestamp, a SQL runtime error will occur. When dragging an Extract Hour function into a variable, the following tree element is created.
Columns and/or other expressions/literals that resolve to a time or timestamp can be moved over the (empty) branch of the tree.
The type of the value returned is integer. There are no special properties for the Extract Hour function.