Join Bill Weinman for an in-depth discussion in this video Removing duplicates with SELECT DISTINCT, part of SQL Essential Training.
…There are times when you may want to know all…the different values of a column in your result without duplication.…For this purpose, SQL provides the select distinct statement.…We're going to start with the world.db database for this lesson.…We're going to change databases Part way through the lesson so…we'll start with the country table and I'm just going to…list all of the continents from the country table like…this: select, continent from country, and I'll press the Go button.…
And you see, there's a list of all of the continent…values in the table, all the values in the continent column.…You notice that we get 239 rows, and there's a…lot of duplication here, Asia, Europe, North America, there's another Europe.…There's another Africa, another North America.…And so we have all of these results, but we…just really want to know how many different continents are represented here.…So the way that you do this is with the select distinct statement.…So, where we have select here, we're just going to add the word distinct.…
- 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.
<div id="pastingspan1">A: This usually means that you have the Apple version of the Apache Web Server already running.</div> <div> </div> <div id="pastingspan1"></div> <div id="pastingspan1">Apple provides a version of the Apache Web Server with OS X. I chose to use XAMPP because it includes PHP and the MySQL server all in one package.</div> <div> </div> <div id="pastingspan1"></div> <div id="pastingspan1">You cannot install XAMPP with Apache already running on your Mac. If you see "It works!" when you open your browser and type "localhost" into the address bar, this means that the Apple version of Apache is already running. You cannot run two instances of a web server at once, so the Apple Apache must be stopped before you can install XAMPP.</div> <div> </div> <div id="pastingspan1"></div> <div id="pastingspan1">In OSX 10.7 and earlier, you could start and stop the Apache Web Server in Control Panel, by choosing "Sharing" and then unchecking the "Web Sharing" checkbox. As of 10.8 this option is no longer in the control panel.</div> <div> </div> <div id="pastingspan1"></div> <div id="pastingspan1">To disable Apple's version of Apache in current versions of OS X, open a Terminal window and type this command:</div> <div> </div> <div id="pastingspan1"></div> <blockquote style="margin: 0 0 0 40px; border: none; padding: 0px;"> <div id="pastingspan1">sudo apachectl stop</div> <div> </div> </blockquote> <div id="pastingspan1"></div> <div id="pastingspan1">You will need to type your system password when prompted, then you should be able to start the XAMPP version of Apache.</div>
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?
<p>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: </p> <blockquote style="margin: 0px 0px 0px 40px; border: none; padding: 0px;"> <p> </p><ol> <li>Open a Finder window and Navigate to /Applications/XAMPP/htdocs/SQL</li> <li>Control-click on the SQL folder and select "Get Info" from the context menu. </li> <li>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. </li> <li>Now repeat the process for the three *.db files inside the folder. </li> </ol> <p> </p> </blockquote>
1. SQL Quick Start
Understanding joins2m 23s
Dates and times1m 59s
10. Subselects and Views
11. A Simple CRUD Application
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