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Function to convert date from text format YYYYDDD where DDD = number of days in the year

Posted on 2007-11-20
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Last Modified: 2008-03-03
eg. select dbo.CnvDateYYYYDDD('2007305')  will return 31-Oct-2007

Thanks



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Question by:xenium
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14 Comments
 

Author Comment

by:xenium
ID: 20322507
i should say, where DDD = day of year !
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LVL 143

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 20322514
replace(convert(varchar(10), convert(datetime, '2007305', 112), 106), ' ', '-')
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LVL 143

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 20322562
sorry, posted to fast...

create function dbo.CnvDateYYYYDDD(@v varchar(7))
returns varchar(11)
as
begin
 declare @d datetime
 declare @res varchar(11)
 set @d = dateadd(day, cast(right(@v, 3) as int) -1, convert(datetime, left(@v,4) + '01-01', 120))
 set @v = replace(convert(varchar(11), @v, 106), ' ', '-')
 return @v
end

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Author Comment

by:xenium
ID: 20322615
select dbo.CnvDateYYYYDDD('2007305')

Server: Msg 241, Level 16, State 1, Procedure CnvDateYYYYDDD, Line 7
Syntax error converting datetime from character string.


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Author Comment

by:xenium
ID: 20322730
this seems to work (several edits!)..

create function dbo.CnvDateYYYYDDD(@v varchar(7))
returns varchar(11)
as
begin
 declare @d datetime
 declare @res varchar(11)
 set @d = dateadd(day, cast(right(@v, 3) as int)-1, convert(datetime, left(@v,4) + '-01-01', 120))
 set @res = replace(convert(varchar(11), @d, 106), ' ', '-')
 return @res
end

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Author Comment

by:xenium
ID: 20322742
Correction also, select dbo.CnvDateYYYYDDD('2007305') correctly returns 1st-Nov-2007
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Author Comment

by:xenium
ID: 20322780
Thanks for helping get the solution. Copy-paste the above corrected function for the points (just makes PAQ simpler)
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LVL 143

Accepted Solution

by:
Guy Hengel [angelIII / a3] earned 500 total points
ID: 20322797
I see I had
 set @res = replace(convert(varchar(11), @v, 106), ' ', '-')

instead of
 set @res = replace(convert(varchar(11), @d, 106), ' ', '-')

sorry for that typo, I wrote the code directly here without checking..
create function dbo.CnvDateYYYYDDD(@v varchar(7))
returns varchar(11)
as
begin
 declare @d datetime
 declare @res varchar(11)
 set @d = dateadd(day, cast(right(@v, 3) as int)-1, convert(datetime, left(@v,4) + '-01-01', 120))
 set @res = replace(convert(varchar(11), @d, 106), ' ', '-')
 return @res
end

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LVL 70

Expert Comment

by:Scott Pletcher
ID: 20322837
Functions should be written *for efficiency* -- no extraneous variables, code, etc. -- rather than to show step-by-step logic.  For example:
CREATE FUNCTION dbo.CnvDateYYYYDDD(
    @yyyyddd varchar(7)
)
RETURNS varchar(11)
AS
BEGIN
RETURN REPLACE(CONVERT(VARCHAR(11), 
    DATEADD(DAY, CAST(RIGHT(@yyyyddd, 3) AS INT) - 1, LEFT(@yyyyddd, 4) + '0101')
    , 106), ' ', '-')
END

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Author Comment

by:xenium
ID: 20323005
Scott, thanks for the suggestion, i agree efficiency is important. Though in many cases human efficiency is more valuable than machine efficiency, so clearer coding may be preferred.
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LVL 70

Expert Comment

by:Scott Pletcher
ID: 20323254
>>  Though in many cases human efficiency is more valuable than machine efficiency <<

I wouldn't recommend that for functions -- you could end up noticeably slowing down your system.  When you start applying a function to every row of a table, efficiency can make a *big* difference, especially when the table goes from 100 rows to 100,000 or 1M rows for some reason.
0
 
LVL 143

Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 20323298
I do agree with ScottPletcher.
you should consider writing the function with the most effective code, and comment with the more human-readable version...
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Author Comment

by:xenium
ID: 20324137
Ok thanks, fair point. Follow-up 1 coming up, as i need the output as Datetime..
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Author Comment

by:xenium
ID: 20324150
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