This is probably why the ANSI SQL standard specifies that
the way to get an INTERVAL from two timestamps is to subtract
them within parentheses follow that with interval_qualifier. Under
the standard you are required to SAY whether you want the
interval in days or hours, etc.

*interval_value_expression
: interval_term
;

*interval_qualifier
: start_field TK_to end_field

*single_datetime_field
: non_second_datetime_field [ LEFT_PAREN
interval_leading_field_precision RIGHT_PAREN ]
;

*non_second_datetime_field
: TK_year

*interval_leading_field_precision
: UNSIGNED_INTEGER
;

*interval_fractional_seconds_precision
: UNSIGNED_INTEGER
;

When you do a subtraction, it isn't clear if you are
interested in "days" or "hours"

---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match