SQL Text to Date error

I have a text column called readdate which is text(6).  It is actually a date that is formatted yymmdd.  I need to convert this column to date.  Here is what I have:

Use HDB
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SELECT CUSTOMER
      ,convert(date,readdate,12) as DATEOFREAD
FROM openquery(UDB,'select * FROM ATABLE');

While it is executing, DATEOFREAD comes up with the format of XXXX-XX-XX, but then errors with this:

Conversion failed when converting date and/or time from character string.

Any suggestions?
Scott AbrahamTechnical Systems ManagerAsked:
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Steve WalesSenior Database AdministratorCommented:
Check CAST and CONVERT doco: http://msdn.microsoft.com/en-us/library/ms187928.aspx

My guess is that the format you are using doesn't match the data string.

Format of 12 is yymmdd

Format of yyyymmdd would be 112.

YYYY-MM-DD in and of itself doesn't appear to be supported.

You could try format 120 - but it may require a time component, not sure it will accept the date without the time component (and not in a position to test that just at the moment).
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Phillip BurtonDirector, Practice Manager and Computing ConsultantCommented:
If you are using SQL Server 2012 or 2014, use Try_Convert instead of Convert; this will return Null if it doesn't succeed, allowing you to diagnose the error further.
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PortletPaulEE Topic AdvisorCommented:
varchar(6) can hold information that isn't a date., e.g. the 31st of September
| READDATE | READDATE_DATE |
|----------|---------------|
|   140901 |    2014-09-01 |
|   140930 |    2014-09-30 |
|   140931 |        (null) |
|   141001 |    2014-10-01 |
|   141023 |    2014-10-23 |
|   141031 |    2014-10-31 |

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Try either of these:
select
        readdate
      , case when isdate(readdate) = 1 then convert(date,readdate,12) end AS readdate_date
from atable
;

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select
        readdate
      , ca.readdate_date
from atable
cross apply (
            select case when isdate(readdate) = 1 then convert(date,readdate,12) end
            ) AS ca (readdate_date)
;

Open in new window

Using CROSS APPLY is particularly useful if you need to do some more calculations with the converted date in the same query as you can refer to it by the column alias.

setup details
**MS SQL Server 2012 Schema Setup**:

    
    
    CREATE TABLE ATABLE
    	([readdate] varchar(6))
    ;
    	
    INSERT INTO ATABLE
    	([readdate])
    VALUES
    	('140901'),
    	('140930'),
    	('140931'),
    	('141001'),
    	('141023'),
    	('141031')
    ;

**Query 1**:

    
    select
            readdate
          , case when isdate(readdate) = 1 then convert(date,readdate,12) end AS readdate_date
    from atable
    

**[Results][2]**:
    
    | READDATE | READDATE_DATE |
    |----------|---------------|
    |   140901 |    2014-09-01 |
    |   140930 |    2014-09-30 |
    |   140931 |        (null) |
    |   141001 |    2014-10-01 |
    |   141023 |    2014-10-23 |
    |   141031 |    2014-10-31 |


**Query 2**:

    select
            readdate
          , ca.*
    from atable
    cross apply (
      select case when isdate(readdate) = 1 then convert(date,readdate,12) end
      ) ca (readdate_date)
    

**[Results][3]**:
    
    | READDATE | READDATE_DATE |
    |----------|---------------|
    |   140901 |    2014-09-01 |
    |   140930 |    2014-09-30 |
    |   140931 |        (null) |
    |   141001 |    2014-10-01 |
    |   141023 |    2014-10-23 |
    |   141031 |    2014-10-31 |



  [1]: http://sqlfiddle.com/#!6/b3b45/3

  [2]: http://sqlfiddle.com/#!6/b3b45/3/0

  [3]: http://sqlfiddle.com/#!6/b3b45/3/1

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Scott AbrahamTechnical Systems ManagerAuthor Commented:
Worked great!!
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