The HOUR function returns the hour part of a value.

>>-HOUR--(--expression--)--------------------------------------><
- expression
- An expression that returns a value of one of
the following built-in data types: a time, a timestamp, a character string,
a graphic string, or a numeric data type.
- If expression is a character or graphic string,
it must not be a CLOB or DBCLOB and its value must be a valid string representation
of a time or timestamp. For the valid formats of string representations of
times and timestamps, see String representations of datetime values.
- If expression is a number, it must be a time
duration or timestamp duration. For the valid formats of datetime durations,
see Datetime operands and durations.
The result of the function is a large integer. If the argument
can be null, the result can be null; if the argument is null, the result is
the null value.
The other rules depend on the data type of the argument:
- If the argument is a time, timestamp, or valid character-string representation
of a time or timestamp:
The result is the hour part of the value, which
is an integer between 0 and 24.
- If the argument is a time duration or timestamp duration:
The result
is the hour part of the value, which is an integer between -99 and 99. A nonzero
result has the same sign as the argument.