Working with UTC (Coordinated Universal Time) in SQL can be a bit tricky, especially if you need to convert it to different time zones, like EST (Eastern Standard Time) for instance. It’s even trickier when you consider daylight saving time. However, with the right understanding and application of functions, the task becomes easier. An important part of this task is understanding the concepts of UTC and EST and how they relate to each other.
Understanding UTC and EST
UTC, short for Coordinated Universal Time, is the time standard that the world uses to set their clocks. It is considered as the base time from which all other timezones are calculated. On the other hand, EST refers to Eastern Standard Time, which is UTC-5. Meaning, it’s five hours behind UTC. However, during daylight saving time, it becomes UTC-4.
When converting between these two timezones, you’ll need to use specific SQL functions and cater for the daylight saving time as well.
SQL Functions for Time Conversion
To convert UTC to EST in SQL, you would generally use the DATEADD function. This function adds a specific value to a date or time part of a date. Here is an SQL snippet for this:
SELECT DATEADD(hh, -5, GetUTCDate())
In this example, GetUTCDate() gets the current UTC date and time, and the DATEADD function subtracts 5 hours from it to convert it into EST.
Handling Daylight Saving Time
The complication arises from the fact that Eastern Standard Time becomes Eastern Daylight Time (EDT) for part of the year. EDT is only 4 hours behind UTC. Therefore, a means to adjust for this fact is necessary when making conversions.
For example, this code snippet accounts for daylight saving time:
SELECT
CASE
WHEN DATEADD(hh, -5, GetUTCDate()) BETWEEN
(SELECT DATEADD(hh, -5, dateadd(dd, 0-datediff(dd, 0, GetUTCDate()),
dbo.GetDaylightSavingsSwitchPoint_ForYear(DATEPART(YEAR,GetUTCDate()),1)))) AND
(SELECT DATEADD(hh, -5, dateadd(dd, 0-datediff(dd, 0, GetUTCDate()),
dbo.GetDaylightSavingsSwitchPoint_ForYear(DATEPART(YEAR,GetUTCDate()),2))))
THEN DATEADD(hh, -4, GetUTCDate()) ELSE DATEADD(hh, -5, GetUTCDate())
END AS EST
The tricky part about this code is the need to determine the exact times and dates daylight saving time starts and ends, which changes from year to year. This requires more advanced SQL expertise.
Application: Scheduling and Record Keeping
Understanding how to convert UTC to EST in SQL is particularly useful when dealing with scheduling systems, records keeping, and any program that handles date and time. Applications of such conversions include booking systems, banking systems, logging events across different time zones, just to mention a few.
It’s also key in ensuring accurate keeping of historical data, as it ensures that the time kept is uniform regardless of time zone variations.
Other Timezone Conversions
In addition to converting UTC to EST, you may also need to convert UTC to other time zones. Similar to the above, you will also use the DATEADD function, the difference being the number of hours you add or subtract from the UTC date and time.
Remember, understanding these timezone conversions and being able to accurately apply them is a must-have skill for any SQL developer, especially if your application handles data from different geographic locations.
