Join Bill Weinman for an in-depth discussion in this video Creating a joined view, part of SQL Essential Training.
A view can be a simple straight query or it can be a more complex joined query. The technique is the same. For this movie, we'll be using the album.db database. And we'll start with a query that shows all the tracks for each album with the duration in minutes and seconds. We're just going to grab that from the Exercise File for Chapter 10. And we'll paste that into our SQL box here. And there's the result of the query. And the query itself. We've seen this before, it's pretty straightforward JOIN on album ID.
Now, I can save this as a view, and I do that just by saying CREATE VIEW joinedAlbum AS. Then, down here at the end, I'll just SELECT star FROM joinedAlbum semicolon. And our result there is the same, except, now, it's coming from Query 2, which is that SELECT star from joinedAlbum. I can take out all of this. And we get exactly the same result. And in fact, I can use this just as I would any SELECT statement.
I can put a WHERE clause in it. And just get the Jimi Hendrix rows. Or we can use it with a conditional expression to display the duration and time notation. I'm going to grab that here from the exercise files. That one looks like this, because we're treating that joinedAlbum view just as we would a table. I can select particular columns from it. I can use expressions with it. And when I press Go here, you see, we have this whole other view with the duration as minutes and seconds.
That's because of this conditional expression. And again, when I'm done with this view, I can delete it with the DROP VIEW. And, of course, that doesn't affect the underlying tables at all, it just deletes the view. So, any SELECT statement at all can be saved as a view. Views are a fairly standard feature across systems and platforms. You can check your documentation for any additional features, but mostly, views will work the same on any modern database system.
- 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.