Sql-server – updating the entire column with datetime values based on other values in the row

casedatetimesql serversql-server-2008update

I have a very large table [server].[dbo].[MyTable] where I need the SQL statement to fill the column 'ToDateTime' (currently full of NULLs) according to the following logic:

Only add a value to 'ToDateTime' on rows where AID equals 123 and PID equals 2. (rows 2, 4, 5, and 7 below) – otherwise leave 'ToDateTime' as NULL.
If the above condition is met, set/leave 'ToDateTime' as NULL if the data (varchar) cannot be converted to datetime (rows 5 and 7 below have data that will fail datetime conversion)
But if it does contain a value that can be converted to datetime (rows 2 and 4), convert it and update the value in ToDateTime with that converted value.

BEFORE:

ID | AID | PID | ContainedData        | ToDateTime
_________________________________________________
1  | 123 |  1  | xxxx                 | NULL
2  | 123 |  2  | 7/21/2015 8:15:06 AM | NULL
3  | 234 |  2  | xyxy                 | NULL
4  | 123 |  2  | 19/07/2015 12:29:42  | NULL
5  | 123 |  2  | NULL                 | NULL
6  | 345 |  3  | zzzz                 | NULL
7  | 123 |  2  | badTimeString        | NULL

AFTER:

ID | AID | PID | ContainedData        | ToDateTime
_________________________________________________
1  | 123 |  1  | xxxx                 | NULL
2  | 123 |  2  | 7/21/2015 8:15:06 AM | 2015-07-21 08:15:06.000
3  | 234 |  2  | xyxy                 | NULL
4  | 123 |  2  | 19/07/2015 12:29:42  | 2015-07-19 12:29:42.000
5  | 123 |  2  | NULL                 | NULL
6  | 345 |  3  | zzzz                 | NULL
7  | 123 |  2  | badTimeString        | NULL

I have been trying a query similar to what is below but it is filling ToDateTime with the same values for every row (in the case of my actual data, NULL.) I'm not sure if something similar to this query is the right approach, or if I'm way off.

UPDATE MyTable SET ToDateTime =
CASE
WHEN ISDATE(myT.cd)= 1 
THEN CONVERT(DATETIME, myT.cd)
ELSE NULL END
FROM (
 SELECT ContainedData cd
 FROM MyTable
 WHERE [AID] = 123 AND [PID] = 2
 ) myT

Best Answer

It looks like you have at least two different regional date formats there, possibly USA and Europe? You could just split the updates by languages...

something like this, which uses the language setting to control isdate and convert.

set language english;
update test_dates 
set ToDateTime = convert(datetime,ContainedData)
where AID='123' and PID='2' and isdate(ContainedData)=1;

set language british;
update test_dates 
set ToDateTime = convert(datetime,ContainedData)
where AID='123' and PID='2' and isdate(ContainedData)=1;

If the table is too large to update in big chunks, then you should look at wrapping that in a loop with a row limit and a transaction around each update and repeat until zero rows have been updated.

Related Solutions

Mysql – What happens when we take a timediff between timestamp and datetime

In addition to Rolando's answer, please note that a TIMESTAMP column is timezone-aware, while DATETIME is not.

If you don't have multiple time zones, then you're OK; but still, if ever you wanted to convert to other timezones, the TIMESTAMPDIFF calculation will provide with corrupted results.

Sql-server – set date value based on other row values

You can calculate the Delay in a cross apply and use dateadd() to add it to st_date in the main query.

select D1.Split3_ID,
       D1.CU_ID,
       D1.order_id,
       D1.st_date,
       D1.sku,
       D1.Priority,
       D1.Delay,
       dateadd(day, D2.Delay, cast(D1.st_date as date)) as CourseDate
from dbo.set_dates as D1
  cross apply (
              select isnull(sum(D2.Delay), 0)
              from dbo.set_dates as D2
              where D1.order_id = D2.order_id and
                    D1.st_date = D2.st_date and
                    D1.Priority > D2.Priority
              ) as D2(Delay)

SQL Fiddle

Update:

I am not really sure how you want to deal with different st_date within a order_id. The above query groups on order_id and st_date but I guess an alternative would be to use the lowest st_date per order_id in the dateadd function.

select D1.Split3_ID,
       D1.CU_ID,
       D1.order_id,
       D1.st_date,
       D1.sku,
       D1.Priority,
       D1.Delay,
       dateadd(day, D2.Delay, cast(isnull(D2.st_date, D1.st_date) as date)) as CourseDate
from dbo.set_dates as D1
  cross apply (
              select isnull(sum(D2.Delay), 0), 
                     min(D2.st_date)
              from dbo.set_dates as D2
              where D1.order_id = D2.order_id and
                    D1.Priority > D2.Priority
              ) as D2(Delay, st_date)
order by D1.Split3_ID

Update 2:

The update statement for the second query could look like this.

with C as
(
select D1.CourseDate,
       dateadd(day, D2.Delay, cast(isnull(D2.st_date, D1.st_date) as date)) as NewCourseDate
from dbo.set_dates as D1
  cross apply (
              select isnull(sum(D2.Delay), 0), 
                     min(D2.st_date)
              from dbo.set_dates as D2
              where D1.order_id = D2.order_id and
                    D1.Priority > D2.Priority
              ) as D2(Delay, st_date)
)
update C
set CourseDate = NewCourseDate

Update 3:

Or even like this if st_date is guaranteed to be the same within one order_id.

update D1
set CourseDate = dateadd(day, (select isnull(sum(D2.Delay), 0)
                               from dbo.set_dates as D2
                               where D1.order_id = D2.order_id and
                                     D1.Priority > D2.Priority), D1.st_date)
from set_dates as D1

Best Answer

Related Solutions

Mysql – What happens when we take a timediff between timestamp and datetime

Sql-server – set date value based on other row values

Related Question