Sql server® 2012 t-sql fundamentals

 

CHAPTER 2

 

Single-Table Queries

 

 79

You get the following output.

----------------------- 

1900-01-01 12:30:15.123

Suppose you have a table with a column called tm of a DATETIME data type and you store all val-

ues by using the base date. Again, this could be enforced with a CHECK constraint. To return all rows 

for which the time value is 12:30:15.123, you use the filter WHERE tm = ‘12:30:15.123’. Because you 

did not specify a date component, SQL Server assumes that the date is the base date when it implic-

itly converts the character string to a DATETIME data type.

If you want to work only with dates or only with times, but the input values you get include both 

date and time components, you need to apply some manipulation on the input values to “zero” the 

irrelevant part. That is, set the time component to midnight if you want to work only with dates, and 

set the date component to the base date if you want to work only with times. I’ll explain how you can 

achieve this shortly, in the “Date and Time Functions” section.