Join Bill Weinman for an in-depth discussion in this video Creating a view, part of SQL Essential Training.
In SQL you can save a query as a view. This is really very simple. For this lesson, we're going to be using the album.db database. And I'm going to start with a simple query here. This is all from the track table. I'm taking the duration as minutes ans seconds by performing integer division and a modulus operation. And now when I press go, you see we have this track table, but it has the durations split into minutes and seconds. I think that's pretty useful, and I'm going to use it again. So I want to make this into a stored view.
And all that does is it stores this select statement in the database so that it can be used again. And I'll just indent the query a little bit, and then I'll select it using the view. Now if you remember, the result of a select statement, is effectively a table, and so we've created a view which is basically just storing this select statement. And now that can be used anywhere you would use a table. So there's our view. And if I delete this and just do SELECT FROM trackView, you see we have exactly the same result.
That trackView is not basically a stored version of that SELECT statement. Now, because SELECT is effectively a table, I can use trackView anywhere I would use a table. I can do something like this. I'm using a joint select with the album on the left, and the track view on the right. And I can say order by. I need the on for my joint, so that's like this. And I can order by a dot title, and within that t dot track number. So, I'm just using that track view as if it were the right hand table in the drawing.
And there's my result. And you see I have my minutes and seconds over here. So there I'm using the view just as I would any other table. Now when you're done with the view, you ca delete it with drop, just like this. Drop view. And that deletes the view, it does not affect the underlying tables at all, it just deletes the view. So view is really just a safe query. Because the result of a select is effectively a table you can use the view. Anywhere where you would use a table. I'll show you a more complex example in the next lesson.
- 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.