在ORACLE SQL中使用带小数的替代

Question

I need to substract 2 timestamps in the given format:

16/01/17 07:01:06,165000000 
16/01/17 07:01:06,244000000

I want to express the result with 2 decimal values but somewhere in the CAST process I am loosing precision. My atempt by now goes this way:

select 
  id,
  trunc((CAST(MAX(T.TIMESTAMP) AS DATE) - CAST(MIN(T.TIMESTAMP) AS DATE))*24*60*60,2) as result 
from table T
group by id;

But I get id_1 '0' as a result for the two timestamps above even after I set the truncate decimals at 2.

Is there a way that I can obtain the 0.XX aa a result of the substraction?

Answer 1

It's because you are casting the timestamp to date.

Use to_timestamp to convert your string into timestamp.

Try this:

with your_table(tstamp) as (
  select '16/01/17 07:01:06,165000000' from dual union all
  select '16/01/17 07:01:06,244000000' from dual
),
your_table_casted as (
    select to_timestamp(tstamp,'dd/mm/yy hh24:mi:ss,ff') tstamp from your_table
)
select trunc(sysdate + (max(tstamp) - min(tstamp)) * 86400 - sysdate, 2) diff 
from your_table_casted;

The difference between two timestamps is INTERVAL DAY TO SECOND .

To convert it into seconds, use the above trick.

Answer 2

DATE—This datatype stores a date and a time, resolved to the second. It does not include the time zone. DATE is the oldest and most commonly used datatype for working with dates in Oracle applications.

TIMESTAMP—Time stamps are similar to dates, but with these two key distinctions: you can store and manipulate times resolved to the nearest billionth of a second (9 decimal places of precision), and you can associate a time zone with a time stamp, and Oracle Database will take that time zone into account when manipulating the time stamp.

The result of a substraction of two timestamps is an INTERVAL:

INTERVAL—Whereas DATE and TIMESTAMP record a specific point in time, INTERVAL records and computes a time duration. You can specify an interval in terms of years and months, or days and seconds.

You can find more information here