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SQL syntax to delelte data is not a date format

Posted on 2016-09-04
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Last Modified: 2016-09-05
I am importing data from a third party software
One of the fields they have is an nvarchar(200) but holds dates in format :  mm/dd/yyyy

Most of the entries in that field are in fact dates, but some aren't. I need to delete any entries in that field which are NOT a 'date' or in date format 'mm/dd/yyyy'

The table name is:  Dependents
The field name is:  DepLastUSEntry

Also some dates are in :  07/27/03

Can they be converted to :  07/27/2003  ?
And also:  8/25/2003  into 08/25/2003  
Maybe:  8/13.2002  into 08/13/2002

Anything different that cannot be converted into a mm/dd/yyyy should be deleted, and if the conversions above cannot be done then remove any date that is not mm/dd/yyyy




Thanks!
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Question by:Aleks
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7 Comments
 
LVL 30

Expert Comment

by:Olaf Doschke
ID: 41783867
Which SQL Server version are you using (SELECT @@Version)?

Starting wioth 2012 you may use:

SET LANGUAGE ENGLISH -- importatnt to process dates in format mm/dd/yyyy, might be optional if your server setting is in english/british/us format anyway.
DELETE FROM yourtable WHERE TRY_CONVERT(date, DepLastUSEntry) IS NULL

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Just try some dates (especially with day>12) on try_convert to see whether it results in a date for correct nvarchar strings, so you don't delete everything.

Bye, Olaf.
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LVL 66

Expert Comment

by:Jim Horn
ID: 41783891
>I need to delete any entries in that field which are NOT a 'date' or in date format 'mm/dd/yyyy'
DELETE means remove the entire row from the table.
UPDATE means change values in the row, say changing this column to an empty string or NULL '', and keep the row.

Tell us which you wish to do here.
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Author Comment

by:Aleks
ID: 41783895
Sorry. I meant update and make it null
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LVL 30

Expert Comment

by:Olaf Doschke
ID: 41783898
Well, then you would UPDATE instead of delete, but you can't update an nvarchar column with a date, you can only set those NULL, which aren't a date in string form.

SET LANGUAGE ENGLISH -- important to process dates in format mm/dd/yyyy, might be optional if your server setting is in english/british/us format anyway.
UPDATE yourtable SET DepLastUSEntry = NULL 
WHERE TRY_CONVERT(date, DepLastUSEntry) IS NULL

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Again, test before you do, with the wrong settings (eg TRY_CONVERT converting dd/mm/yyyy instead of mm/dd/yyyy, international formats differ a lot also in regard of the dash separator) you may lose part of the dates you rather wanted to keep.

If your overall goal is to alter the table to have a date or datetime column:

Set Language English;
Create Table #Test (DepLastUSEntry nvarchar(200));
Insert Into #Test Values (N'12/31/2010'), (N'31/12/2015');
Select * From #Test;

Update #Test set DepLastUSEntry = NULL WHERE TRY_CONVERT(date,DepLastUSEntry) IS NULL;

Alter Table #Test Alter Column DepLastUSEntry Date NULL;
Select * From #Test;
Drop Table #Test;

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You would execute lines 1, 6, and 8 only, obviously.

Bye, Olaf.
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Author Comment

by:Aleks
ID: 41784584
I tried this, but I am using SQL 2008R2

SET LANGUAGE ENGLISH -- important to process dates in format mm/dd/yyyy, might be optional if your server setting is in english/british/us format anyway.
UPDATE yourtable SET DepLastUSEntry = NULL 
WHERE TRY_CONVERT(date, DepLastUSEntry) IS NULL

Open in new window


Error

Msg 195, Level 15, State 10, Line 5
'TRY_CONVERT' is not a recognized built-in function name.

Open in new window

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LVL 30

Accepted Solution

by:
Olaf Doschke earned 2000 total points
ID: 41784730
That's why I asked for the version. Then try it with ISDATE():

First see, if these dates are correct:
SELECT DepLastUSEntry FROM yourtable WHERE ISDATE(DepLastUSEntry)=1

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If so, this update will change all other invalid ones to NULL:
UPDATE yourtable SET DepLastUSEntry = NULL 
WHERE ISDATE(DepLastUSEntry)=0

Open in new window

Bye, Olaf.
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Author Closing Comment

by:Aleks
ID: 41784953
This worked!
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