Convert ISO8061 Duration to a datetime or time value - sql-server

Question

I have some ISO8601 Durations (not to be confused with ISO601 datetime)
Here are some example valid values:
P1D
PT0H
PT11M
P1DT2H15M
PT10H11M
PT2H46M12S
the specification is here:
https://en.wikipedia.org/wiki/ISO_8601#Durations
Ideally, I would like to take these values and parse them as either time or datetime2 values
to make it easier to work with
I was able to brute force parse these using string functions but the code is complex and seems error prone hoping there was a better way?
with anchors as
(
SELECT
dt[duration]
, NULLIF(CHARINDEX('D', dt.duration), 0) As DLocation
, NULLIF(CHARINDEX('T', dt.duration), 0) As TLocation
, NULLIF(CHARINDEX('H', dt.duration), 0) As HLocation
, NULLIF(CHARINDEX('M', dt.duration), 0) As MLocation
, NULLIF(CHARINDEX('S', dt.duration), 0) As SLocation
, LEN(dt.duration) as TotalLength
FROM dbo.DurationTest dt
)
SELECT
duration
,DaysValue = CAST(ISNULL(SUBSTRING(duration, 2, (DLocation - 2)), 0) as tinyint)
,HoursValue = CAST(ISNULL(SUBSTRING(duration, TLocation + 1, (HLocation - TLocation) - 1 ), 0) as tinyint)
,MinutesValue = CAST(ISNULL(SUBSTRING(duration, COALESCE(HLocation, TLocation) + 1, MLocation - COALESCE(HLocation, TLocation) - 1), 0) as tinyint)
,SecondsValue = CAST(ISNULL(SUBSTRING(duration, COALESCE(MLocation, TLocation) + 1, SLocation - COALESCE(MLocation, TLocation) - 1 ), 0) as tinyint)
FROM anchors
this code gets the values into days, hours, minutes and seconds. converting to either a int value to seconds or a datetime2 is pretty well documented from that. As pointed out in the comments a time data type will only work for values <24 so I've kind of given up on that.
for further context this data is coming from ADP payroll webservice and this field tracks the daily time entry you would think it would be less than 24hrs but I have some outliers in my dataset.
I've created the following enhancement request here (not sure if it will get traction or not):
https://feedback.azure.com/d365community/idea/557e5b51-1824-ed11-a81b-6045bd853198

Answer 1

Here's one working example. Read the header for what it does but this one returns the ADP "ISO-Like" durations as Decimal Hours to 6 Decimal Places. If you need something else instead, the changes will be quite simple to make. Let me know.
Here's the iTVF (inline Table Valued Function). Details are in the comments. As so often happens, the comments are bigger than the code itself.
CREATE FUNCTION dbo.AdpDurToDecHours
/*********************************************************************
Purpose:
Convert ADP payroll webservice daily time entries (durations) from a
subset of the ISO Duration notation to Decimal Hours.
*** DO NOT USE THIS FUNCTION IF YEAR AND/OR MONTH CAN BE PRESENT! ***
----------------------------------------------------------------------
Usage Examples:
--===== Convert a set of ADP time entries from a table.
SELECT st.SomeOtherColumns
,adp.DecimalHours
FROM dbo.SomeTable st
CROSS APPLY dbo.AdpDurToDecHours(st.AdpDur) adp
;
--===== Convert a single value from a variable.
SELECT adp.DecimalHours FROM dbo.AdpDurToDecHours(#AdpDur) adp
;
----------------------------------------------------------------------
Dependencies:
1. None
----------------------------------------------------------------------
Programmer Notes:
1. DO NOT USE THIS FUNCTION IF YEAR AND/OR MONTH CAN BE PRESENT!!!
2. This code will fail with the following error if you pass it a
NULL, Empty String, or BLANK String. Other "non-ISO" compliant
values may also fail or create improper output but such other
things have not been tested. Ostensibly, the values passed should
be compliant for proper returns.
Msg 1014, Level 15, State 1, Line 30
A TOP or FETCH clause contains an invalid value.
3. This code follows the ISO specification for durations except for
"Year" and "Month", which have been intentionally excluded because
they're "indeterminate" for durations unless combined with a
starting date.
----------------------------------------------------------------------
References:
1. https://en.wikipedia.org/wiki/ISO_8601#Durations
2. https://stackoverflow.com/questions/73479091/convert-iso8061-duration-to-a-datetime-or-time-value
----------------------------------------------------------------------
Revision History:
Rev 00 - 25 Aug 2022 - Jeff Moden
- Create and test PoP code.
Rev 01 - 26 Aug 2022 - Jeff Moden
- Exclude "Year" and "Month".
- Convert output to Decimal Hours.
Rev 02 - 27 Aug 2022 - Jeff Moden
- Convert to documented function (iTVF).
*********************************************************************/
(#AdpDur VARCHAR(36))
RETURNS TABLE WITH SCHEMABINDING
RETURN WITH
--==== Creates an inline sequence generator
S1(N) AS (SELECT 1 FROM (VALUES (1),(1),(1),(1),(1),(1))S0(N))
,cteTally(N) AS (SELECT TOP(LEN(#AdpDur))
N = ROW_NUMBER() OVER (ORDER BY (SELECT NULL))
FROM S1 a,S1) --1 to 36 rows max
,cteLocateDurTypes AS
(--==== Find positions/lagging positions of the duration type tokens
SELECT DurType = SUBSTRING(#AdpDur,t.N,1)
,LN = LAG(t.N,1,0) OVER (ORDER BY t.N)
,t.N
FROM cteTally t
WHERE SUBSTRING(#AdpDur,N,1) IN ('P','W','D','T','H','M','S')
)
,cteIsolateValue AS
(--==== Determine the value for each duration token present
SELECT DurType
,Value = CONVERT(INT,SUBSTRING(#AdpDur,LN+1,N-1-LN))
FROM cteLocateDurTypes
)--==== Convert DurType Values to seconds and sum as Decimal Hours
SELECT DecimalHours = SUM(
CASE DurType
WHEN 'S' THEN Value
WHEN 'M' THEN Value*60
WHEN 'H' THEN Value*3600
WHEN 'D' THEN Value*86400
WHEN 'W' THEN Value*604800
ELSE 0
END
)/3600.0
FROM cteIsolateValue
;
GO
Here's a short test table based on what #JasonHorner posted with a few additions.
--===== Drop the test table if it exists to make reruns easier in SSMS
DROP TABLE IF EXISTS #DurationTest;
GO
--===== Create and populate the test table on-the-fly.
SELECT Duration = CONVERT(VARCHAR(36),v.Duration)
INTO #DurationTest
FROM (VALUES
--(NULL) --Causes Failure
--,('') --Causes Failure
--,(' ') --Causes Failure
('PT') --It could happen
,('P1W') --Added this entry
,('P1D')
,('PT1H') --Added this entry
,('PT1M') --Added this entry
,('PT1S') --Added this entry
,('PT0H')
,('PT10H') --Added this entry
,('PT11M')
,('P1DT2H15M')
,('PT10H11M')
,('PT2H46M12S')
,('P1W2DT12H46M12S') --Added this entry
)v(Duration)
;
GO
Here's a test of the function using the test table as the source.
--===== Simple test
SELECT *
FROM #DurationTest dt
CROSS APPLY dbo.AdpDurToDecHours(dt.Duration) adp
;
GO
And, finally, here are the results from the test.