How to convert CHAR values into DATETIME values in SQL Server

Summary

The following information discusses how to convert CHAR values into DATETIME values so that a SMALLINT value can be subtracted and a START_TIME value can be obtained.

More Information

To begin with, the character date and time must be converted into the SQL Server datetime format. Then the SMALLINT value can be subtracted to obtain START_TIME. Both tasks can be performed in a single SQL expression; however, it is easier to understand the process if both tasks are considered separately.


For example, if the time value is stored in a column named "term_time" with a format of HHMMSS, and the date value is stored in a column named "term_date" with a format of YYMMDD, these values can be converted to the SQL Server datetime with the following call:

   convert(datetime,term_date+" "+
substring(term_time,1,2)+":"+
substring(term_time,3,2)+":"+
substring(term_time,5,2) )

Given a date in SQL Server datetime format, it is easy to add or subtract a given amount of seconds, minutes, days, and so forth. For example, assuming the SMALLINT value ("@delta") is in seconds, the following function will return the start date/time:

   dateadd(ss,-(@delta),???)

The entire expression can be put into the following select statement so it is executed for each row in the input table. "@delta" is assumed to be an input parameter. If "@delta" is in units other than seconds, the first parameter of dateadd must be changed to reflect the correct units (minutes, days, and so forth).

   select  dateadd( ss, -(@delta), convert(datetime,term_date+" "+
substring(term_time,1,2)+":"+
substring(term_time,3,2)+":"+
substring(term_time,5,2) ))
from t1
Propriedades

ID do Artigo: 69133 - Última Revisão: 10 de jul de 2008 - Revisão: 1

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