Join Bill Weinman for an in-depth discussion in this video Deleting data, part of SQL Essential Training.
The delete statement is used to remove rows from a table. In this lesson, I'm starting with the test database, as modified in the previous couple of lessons. So, I'm going to select the test database here. And we'll start by looking at the state of the customer table with select asterisk from customer. Press the Go button and you see we have the original three rows and a couple of rows that we've added. So let's start by deleting the row with the id number four.
When you're typing in a delete statement, it's often a good idea to start with the select statement to make sure that your where clause is exactly right and you're just selecting the rows that you actually want to delete. So, I'm just going to come in here and I'm going to type, where id equals 4, and I'll press the Go button, so you see I've selected just that one row that I actually want to delete. So, I'm going to leave my select statement, I'm actually going to copy and paste it up here, and I'm going to take out the select and the asterisk, going to replace it just with delete.
And then, in my select statement, I'm just going to look at the entire table. So when we're done here. This will delete the row with the id number four and we'll select the entire table so we can see that that row has been deleted. So, I'm going to press Go. And you see up here it says, one row affected. And four rows returned, where we used to have five. And we see the one with the id number four is now gone. Let's also go ahead and delete the Jimi Hendrix row, so that's id equals five.
And I'll press Go and that row is gone now and our test database is back in its original state. The delete statement is very simple, it's used to delete rows from a table, you use the where clause to select the rows to be deleted, just as you did with the update statement to choose the rows to be effected by the update.
- 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.