Join Bill Weinman for an in-depth discussion in this video Date- and time-related functions, part of SQL Essential Training (2014).
Every database system has it's own set of functions specifically tasked for handling dates and times. These functions are not standardized. In this lesson, I'll show you the date and time-related functions for SQL lite, the system we're using for the exercises. Keep in mind that the specific functions and syntax for your system will be different. For this lesson, we're going to use the in memory database. And we'll start with a simple statement. This statement returns a timestamp. The current date and time in the UTC time zone.
A time stamp is a very common usage. And every system has a convenient way of finding the current date and time. The time and date returned is in UTC, seven hours later than my local time in Arizona. SQL lite uses strings for the date and time, so it makes sense that it uses a special string for the current time. Passing the string now to the date time function returns a proper SQL formatted date and time, representing the current UTC time. You can get just the date part by calling the function Date, instead of date time, or you can get just the time part by calling the Time function Different systems perform date and time arithmetic in different ways.
We'll go back to the date time function. And that looks like that. And the way that SQL Lite does it, you pass it one or more extra arguments with the arithmetic operation. For example, I can say, plus 1 day like that. And, instead of January 20th, see, it says January 21st with the same time. I can say three days, and I can use day or I can give it an s, either way it works the same way.
And now it's January 23rd. Or I can say minus 1 month, like that. And now it's December 20th in 2013. Or I can combine multiple arguments for more complex calculations. I can say plus 3 hours, plus 27 minutes, minus 1 day, plus 3 years. And it will combine each of these arguments. Basically, applying each argument to the result of the argument before it.
And we get that result there. As usual, keep in mind that your system will differ, especially with dates and times, you need to consult your documentation to know how your system works.
- Understanding SQL terminology and syntax
- Creating new tables and records
- Inserting and updating data
- Writing basic SQL queries
- Sorting and filtering
- Accessing related tables with JOIN
- Working with strings
- Finding the numeric type of a value
- Using aggregate functions and transactions
- Updating a table with triggers
- Creating views
Skill Level Beginner
Q: For Mac OS X: When I try to start the Apache Web Server from the XAMPP control panel, it doesn't start, and when I open "localhost" in my web browser, I see a white screen that says "It Works!" instead of the XAMPP page.
sudo apachectl stop
Q: I'm on a Mac, and I get an error in SID that says "attempt to write a read only database." How can I fix this?
A: This usually means that the database folder does not have sufficient permissions for writing by the web user. This can happen if you create the SQL folder new, rather than copying it from the Exercise Files. Here's how to fix this:
- Open a Finder window and Navigate to /Applications/XAMPP/htdocs/SQL
- Control-click on the SQL folder and select "Get Info" from the context menu.
- Under "Sharing and Permissions" (you may need to open the disclosure triangle), in the "everyone" row, select "Read & Write."Then you can close the Info window.
- Now repeat the process for the three *.db files inside the folder.