Join Bill Weinman for an in-depth discussion in this video Updating data, part of SQL Essential Training.
The update statement is used to change data in existing rows in a table. In this lesson, I'm starting with the test database, as it was modified in the previous lesson. So, we're going to select the test database here, and if I select all the rows from the customer table you'll see that it has the rows that we added in the previous lesson right there. Now if I want to update one of these rows, I can do that like this. So this is an update statement. You see I specify the table after the keyword update and then I say, set address equals and I give it a list of columns to set.
So I have the set keyword and then a column name and an equal sign, and a value, and then a comma to separate the columns that are being updated, and so zip equals 98056. And then I use a where clause to specify which rows are going to be updated. In this case where ID equals five, and that will just select one row. You see this last one here that has the address as null and the zip is null, so I'm filling in the address and the zip. I left the select statement in so when we press go, we will see our results, and there it is.
That row was updated. Now if I find that I don't like that, or I want to change it, or customer who's moved, I can put in a new address here. I can say 2603 South Washington Street. And the zip is okay. And if I press go, you'll see that that address is updated and that's actually the address where Jimmy Hendrix grew up in the Washington area. There's no house there anymore. The house has been torn down. So you see, you can update a value again using exactly the same syntax.
If I want to, I can make these nulls again, just by putting in the keyword null. Null is a special value that actually means no value. And press go, and now you see those nulls are back. I'll show you more about null later in this course, but this is how you remove values from a column using the special null. The update statement is used to change the data, in particular columns in a table. You can select which rows are affected by using a where clause.
- 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.