Hi,
Lately, I started to see many developer uses timestamp types (like timestamp or timestamp with time zone) wrong especially in time arithmetic.
So as a short reminder, adding and subtracting numbers to/from a DATE value will add/subtract number of days:
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Select Sysdate "TODAY", Sysdate + 1 "TOMORROW", --add 1 day Sysdate - 1 "YESTERDAY", --subtract 1 day Sysdate + (1/24) "ONE HOUR LATER", -- add one - twenty forth day, since a day has 24 hours, it adds 1 hour Sysdate - (1/24) "ONE HOUR BEFORE", -- remove 1 hour Sysdate + (1/(24*60)) "ONE MINUTE LATER", -- add 1 minute, also 24*60=1440 is used frequently Sysdate + (1/(24*60*60)) "ONE SECOND LATER" -- add 1 second, also 24*60*60=86400 is used frequently From Dual; TODAY TOMORROW YESTERDAY ONE HOUR LATER ONE HOUR BEFORE ONE MINUTE LATER ONE SECOND LATER ------------------- ------------------- ------------------- ------------------- ------------------- ------------------- ------------------- 2020-07-28 14:07:38 2020-07-29 14:07:38 2020-07-27 14:07:38 2020-07-28 15:07:38 2020-07-28 13:07:38 2020-07-28 14:08:38 2020-07-28 14:07:39 |
Basically that is all if you use add and subtract of course we have “INTERVAL” data type which I am about to explain.
This usage is not wrong if you work with DATE but if you are using TIMESTAMP types then there is a small side effect.
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Select Systimestamp "TODAY", Systimestamp + 1 "TOMORROW", --add 1 day Systimestamp - 1 "YESTERDAY", --subtract 1 day Systimestamp + (1/24) "ONE HOUR LATER", -- add one - twenty forth day, since a day has 24 hours, it adds 1 hour Systimestamp - (1/24) "ONE HOUR BEFORE", -- remove 1 hour Systimestamp + (1/(24*60)) "ONE MINUTE LATER", -- add 1 minute, also 24*60=1440 is used frequently Systimestamp + (1/(24*60*60)) "ONE SECOND LATER" -- add 1 second, also 24*60*60=86400 is used frequently From Dual; TODAY TOMORROW YESTERDAY ONE HOUR LATER ONE HOUR BEFORE ONE MINUTE LATER ONE SECOND LATER ------------------------------------- ------------------- ------------------- ------------------- ------------------- ------------------- ------------------- 2020-07-28 14:14:21.490000 +03:00 2020-07-29 14:14:21 2020-07-27 14:14:21 2020-07-28 15:14:21 2020-07-28 13:14:21 2020-07-28 14:15:21 2020-07-28 14:14:22 |
so adding and subtracting did their’s job but if you look carefully there is no fractional seconds! Because they are not TIMESTAMP anymore, they are DATE. adding ans subtracting on timestamp types will convert result into a DATE. Let’s check if they are really date:
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Select Dump(sysdate) , Dump(Systimestamp + 0) From Dual; DUMP(SYSDATE) DUMP(SYSTIMESTAMP+0) ---------------------------------- ---------------------------------- Typ=13 Len=8: 228,7,7,28,14,24,5,0 Typ=13 Len=8: 228,7,7,28,14,24,5,0 |
dump is a function that shows you how oracle store that data internally. in this example you can see both Typ number are 13 and 13 is one of date type which Oracle uses and yes there are more than one date type in oracle but they are not visible to us. For example return type of SYSDATE function and a table date column has different types:
An error has occurred. Please try again later. |
as you see table date column type number is 12 not 13. so they are different but it’s not relevant to us right now.
PS: just in case if you wonder how this data is a date:
Typ=13 Len=8: 228,7,7,28,14,27,25,0
(228+(256*7)) = 2020 and rest is just the month day hour minute and second.
if I returned to main subject adding to a timestamp type will convert it to a DATE and if you use this type in your sql like:
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Select * From Orders Where Created_timestamp >= (Systimestamp -1) |
you will be comparing timestamp (created_timestamp column in orders table) with a DATE (systimestamp -1). of course these are convertible types but still Oracle needs to do a convert operation. to avoid that you can use INTERVAL data types.
I found INTERVAL types more clear to myself.
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Select Systimestamp "TODAY", Systimestamp + Interval '1' Day "TOMORROW", --add 1 day Systimestamp + Interval '1' HOUR "ONE HOUR LATER", -- add one - twenty forth day, since a day has 24 hours, it adds 1 hour Systimestamp + Interval '1' MINUTE "ONE MINUTE LATER", -- add 1 minute, also 24*60=1440 is used frequently Systimestamp + Interval '1' SECOND "ONE SECOND LATER" -- add 1 second, also 24*60*60=86400 is used frequently From Dual; TODAY TOMORROW ONE HOUR LATER ONE MINUTE LATER ONE SECOND LATER --------------------------------- ------------------------------------ ------------------------------------ ------------------------------------ ------------------------------------ 2020-07-28 14:36:57.099000 +03:00 2020-07-29 14:36:57.099000000 +03:00 2020-07-28 15:36:57.099000000 +03:00 2020-07-28 14:37:57.099000000 +03:00 2020-07-28 14:36:58.099000000 +03:00 |
as you can see Interval type are so simple and clean. we just write what we want to add or subtract and result is base type what you pass (TIMESTAMP With Time Zone in my example).
this type of interval has a fault to me. you can not pass number of Day/Hour/… as a parameters. this means you can not use “Interval V_Number_of_Days Day” for example but of course there is a solution, INTERVAL functions NumToDSinterval and NumToYMinterval.
NumToDSinterval = Number To DaySecond Interval
NumToYMinterval = Number To Year Month Interval
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Select NumToDSinterval(1, 'DAY'), NumToDSinterval(1, 'HOUR') From dual; NUMTODSINTERVAL(1,'DAY') NUMTODSINTERVAL(1,'HOUR') ----------------------------- --------------------------------------------------------------------------- +000000001 00:00:00.000000000 +000000000 01:00:00.000000000 |
so you can use:
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Select Systimestamp "TODAY", Systimestamp + NumToDSinterval(1, 'Day') "TOMORROW", --add 1 day Systimestamp + NumToDSinterval(1, 'HOUR') "ONE HOUR LATER", -- add one - twenty forth day, since a day has 24 hours, it adds 1 hour Systimestamp + NumToDSinterval(1, 'MINUTE') "ONE MINUTE LATER", -- add 1 minute, also 24*60=1440 is used frequently Systimestamp + NumToDSinterval(1, 'SECOND') "ONE SECOND LATER" -- add 1 second, also 24*60*60=86400 is used frequently From Dual; |
and result will be same with INTERVAL ‘1’DAY/HOUR…. Also please remember that you can use interval types with DATEs too.
hope this helps you in coding.
wish you a great day.