Join Bill Weinman for an in-depth discussion in this video About SQL strings, part of SQL Essential Training.
In standard SQL, a literal string is represented by a series of characters enclosed in single quote marks. Keep in mind that there are some database systems, notably older versions of MySQL, where double quotes may be used instead. This is not standard, but it's common, so it's worth knowing about. If you need to use a single quote in your string, you use two single quotes together to represent the one. Notice the two single quotes in the word Here's in the example. String handling tends to be platform specific with SQL.
A simple thing like concatenating two strings together can be very different on different platforms. For example, this works on MySQL, and this works in Microsoft SQL server, and this works in SQLite. This is actually the standard, but many systems do not support it. String functions also vary a lot from system to system. There are really just a few string functions that are considered standard, and even these are not supported, or are different on different systems.
Fortunately, SQLite supports these functions as close to the standard as possible. In the rest of this chapter, I'll cover some of the more standardized string functions as implemented by SQLite. You'll need to consult the documentation for your system to find out how these and other string functions are implemented on your 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.