Varchar到Datetime的转换-SQL Server

Question

How can I convert a varchar column into a datetime field. The varchar field has the date and time in the below format

t_time
-------
20140314163955

The below doesn't work

CAST(t_time AS datetime)

Thanks in advance.

Answer 1

One option, in order to keep it clean would be to use a function, like the one below:

CREATE FUNCTION CONVERT_DATETIME_STRING_TO_DATE (@StringDate NVARCHAR(14))
RETURNS DATETIME
AS
BEGIN
DECLARE @RESULT DATETIME

SELECT @RESULT = CONVERT(datetime, substring(@StringDate, 0, 9))
SELECT @RESULT = DATEADD(HOUR, CAST(SUBSTRING(@StringDate, 9, 2) AS INT), @RESULT)
SELECT @RESULT = DATEADD(MINUTE, CAST(SUBSTRING(@StringDate, 11, 2) AS INT), @RESULT)
SELECT @RESULT = DATEADD(SECOND, CAST(SUBSTRING(@StringDate, 13, 2) AS INT), @RESULT)

RETURN (@RESULT)
END

The conversion could be done in one SELECT statement, but I think it's better to separate each step of adding hours, minutes, seconds so it's clearer code and easier to maintain.

Then, just call the function from your table, like:

SELECT CONVERT_DATETIME_STRING_TO_DATE(t_time)
FROM myTable

Update:

If you have access only to do SELECT statements, then use something like this:

SELECT DATEADD(SECOND, CAST(SUBSTRING(t_time, 13, 2) AS INT), DATEADD(MINUTE, CAST(SUBSTRING(t_time, 11, 2) AS INT), DATEADD(HOUR, CAST(SUBSTRING(t_time, 9, 2) AS INT), CONVERT(DATETIME, substring(t_time, 0, 9)))))
FROM TABLE

Answer 2

Try this .

DECLARE @s AS VARCHAR(14)
DECLARE @dt AS DATETIME

SET @s = '20140314163955'
SET @dt = CAST(SUBSTRING(@s, 1,8) as datetime)

SELECT DATEADD(Second, 
               CAST(Substring(@s, 13,2) AS INT) ,
               DATEADD(minute,
                       CAST(Substring(@s, 11,2) AS INT) ,
                       DATEADD(hour, 
                               CAST(Substring(@s, 9,2) AS INT), 
                               @dt))) AS [DateTime]