I am going to perpetuate my writing of short articles or tidbits on Transaction SQL date/time functions.
Most, if not all, modern day computer systems collect data which contains dates and times.
Not only is it important to know when a sales order came in, but we should fulfill the request using some type of queue (LIFO). If if was a stack (FIFO) implementation, the first person may never get his order!
Today, I will be exploring the DATEPART() function. This function has 15 different input parameters that can be passed to change the resulting output.
In short, the function takes a date part and date time variables as input returns the part that you want as an integer. I will be concentrating on how to extract the hour (HH) in this article.
The examples below are sample calls to the function. The inputs puts are valid date, null value and a empty string.
-- Functions to get date and time parts as INT
DATEPART(HH, SYSDATETIME()) AS HOUR_A_INT,
DATEPART(HH, NULL) AS HOUR_B_INT,
DATEPART(HH, '') AS HOUR_C_INT
The output from the test is listed below. It is surprising that an empty string returns a value of 0.
HOUR_A_INT HOUR_B_INT HOUR_C_INT
----------- ----------- -----------
17 NULL 0
In summary, pass the date part parameter to extract the hour as an integer from the date time variable.