Join Bill Weinman for an in-depth discussion in this video Deleting rows from a table, part of SQL Essential Training.
The delete from statement is used to delete rows from a table. Here we're going to use the test.db database. In the previous movie we created a table and added some rows to it. And it looks like this. Now you can use a delete from statement to delete a row, like this. I'm going to leave that select statement in so we can see the result. And I'm going to delete from test. I'm going to use a where clause to select the row that I want to delete. I'm going to say where A equals 3.
So that'll be this column here, that has the A equals 3. This one that says beauty in B. And when I press go, you'll see that that column is now gone. Deleting rows is destructive. That is, once they're deleted, they cannot be easily recovered. So if you're typing SQL, as we are here in this tutorial, it's a good idea to preview your where clause with a select statement like this. So I can say. Select star from Test where A equals and I'll put in another number.
I'll say where A equals 1. I'll delete this second Select statement here. And we see that there's two rows that match our condition. Now to delete these rows, I would simply change the Select statement to a Delete statement like this I would say delete from test, where A equals 1, and I'll go ahead and I'll add a select under it. So that we can see the result. Now the rows that have matched that condition are deleted. There's no more rows with A equals 1. We'll cover the Where clause and other filtering techniques later in this chapter.
For now the DELETE FROM statement is used to delete rows from a table. It is very simple and powerful and the result is destructive. Deleted rows cannot be easily recovered. Again I'm going leave this test table here for now and in the next lesson, I'll use it to show you how the special NULL state 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.