Convert varchar column to datetime in sql server - sql

Question

I have a table with following definition and data.
Definition:
CREATE TABLE [dbo].[TestTB]
(
[CREATEDATE] [nvarchar](50) NULL
) ON [PRIMARY]
Data:
10/9/2014
1/26/2015
2/16/2015
When I run the query:
Select
CAST(CREATEDATE AS DATETIME) as CREATEDATE
FROM
[dbo].[TestTB]
It is throwing error:
Msg 241, Level 16, State 1, Line 1
Conversion failed when converting date and/or time from character string.
The above does not work even after running
SET DATEFORMAT dmy
However the following query works fine
DECLARE #data nvarchar(50)
SET #data = ' 10/9/2014 '
Select CAST(#data as DateTime)
Above query returns: 2014-10-09 00:00:00.000
How do I convert a date string (of mm/dd/yyyy format) stored in a column to datetime?

Answer 1

First, if your table column is "DateTime" type than it will save data in this format "2014-10-09 00:00:00.000" no matter you convert it to date or not. But if not so and if you have SQL Server version 2008 or above than you can use this,
DECLARE #data nvarchar(50)
SET #data = '10/9/2014'
IF(ISDATE(#data)>0)
BEGIN
SELECT CONVERT(DATE, #data)
END
Otherwise
DECLARE #data nvarchar(50)
SET #data = '10/9/2014'
IF(ISDATE(#data)>0)
BEGIN
SELECT CONVERT(DATETIME, #data)
END
To Insert into table
INSERT INTO dbo.YourTable
SELECT CREATEDATE FROM
(
SELECT
(CASE WHEN (ISDATE(#data) > 0) THEN CONVERT(DATE, CREATEDATE)
ELSE CONVERT(DATE, '01/01/1900') END) as CREATEDATE
FROM
[dbo].[TestTB]
) AS Temp
WHERE
CREATEDATE <> CONVERT(DATE, '01/01/1900')

Answer 2

DECLARE #data nvarchar(50)
SET #data = ' 10/9/2014 '
SELECT CONVERT(datetime, #data, 101)
SELECT CONVERT(datetime, CREATEDATE, 101) as CREATEDATE
FROM [dbo].[TestTB]
http://www.sqlfiddle.com/#!6/f2103
please check this http://msdn.microsoft.com/en-us/library/aa226054%28SQL.80%29.aspx

Answer 3

Try this out:
SELECT IIF(ISDATE(CREATEDATE) = 1, CONVERT(DATETIME, CREATEDATE, 110), CREATEDATE) as DT_CreateDate
FROM [dbo].[TestTB]
SQL Fiddle Solution

Answer 4

nvarchar to datetime is an implicit conversion, it means you can do this:
declare #strDate nvarchar(50), #myDate datetime
set #strDate = '01/26/2013'
set #myDate = #strDate
But your problem is date format so you have to convert it, but you have to scpecify the format or style and the code of the style you're using is 101 (according to this table) so the secure way:
declare #strDate nvarchar(50), #myDate datetime
set #strDate = '01/26/2013'
set #myDate = CONVERT(DATETIME, #strDate, 101)
You can skip the code but with diferent configuration(server) that code will break.
If you use the ISO style (yyyymmdd) you never would'nt have to worry and the conversion would be implicit:
declare #strDate nvarchar(50), #myDate datetime
set #strDate = '20150421' --ISO style (yyyymmdd)
set #myDate = #strDate