Convert varchar MMDDYYYY to MM/DD/YYYY datetime and select the most recent date only

Question

Okay, so I have kind of a weird issue... the dates in the table have been entered in as string values MMDDYYYY and I'm trying to have the displayed as MM/DD/YYYY in a report and only select the most recent date pertaining to an ID, because some ID's may have multiple dates.

Example of my table:

  ID  |  MyDate  |
------+----------+
  1   | 01302014 |
  1   | 04222014 |
  2   | 01302014 |

What I want to see when I select and insert into a temp table is this:

  ID  |   MyDate  |
------+-----------+
  1   | 4/22/2014 |
  2   | 1/30/2014 |

I know that storing dates as string values is a poor practice especially when storing them as MMDDYYYY, but does anyone have a solution to this nightmare?

EDIT

I forgot to mention that some fields might be NULL. Not sure if that makes a difference or not, but I think it does if I try to flip the dates using Right, Left, Convert.

Solution 1

This question is for almost a year ago, nut probably someone can find it useful.

You need to CONVERT your string to DATE format and use a ROW_NUMBER function to window your result set.

Create table

DECLARE @tbl TABLE(Id INT, myDate VARCHAR(8))

Sample data

INSERT @tbl
SELECT 1  ,  '01302014' UNION ALL
SELECT 1  ,  '04222014' UNION ALL
SELECT 2  ,  '01302014'

Query

;WITH C AS(
    SELECT  ROW_NUMBER() OVER (PARTITION BY Id ORDER BY CONVERT(DATETIME, (SUBSTRING(myDate, 5, 4) + '.' + SUBSTRING(myDate, 1, 2) + '.' + SUBSTRING(myDate, 3, 2)), 101) DESC) AS Rn
            ,Id
            ,CAST(CONVERT(DATETIME, (SUBSTRING(myDate, 5, 4) + '.' + SUBSTRING(myDate, 1, 2) + '.' + SUBSTRING(myDate, 3, 2)), 101) AS DATE) AS myDate
    FROM @tbl
)
SELECT Id, myDate
FROM C
WHERE Rn = 1

SQLFiddle Demo

Solution 2

Using a CONVERT like the following code snippet will work on any SQL Server regardless of language and/or locale configuration.

DECLARE @OldDate varchar(8); 
SELECT @OldDate = '04252012';

SELECT CONVERT(datetime, substring(@OldDate,5,4) + '-' + substring(@OldDate,1,2) + '-' + substring(@OldDate,3,2) + 'T00:00:00')