SQL ORDER BY
Starting here? This lesson is part of a full-length tutorial in using SQL for Data Analysis. Check out the beginning.
In this lesson we'll cover:
- Sorting data with SQL ORDER BY
- Ordering data by multiple columns
- Using comments
- Practice problems
- What's next?
Once you've learned how to filter data, it's time to learn how to sort data. The
ORDER BY clause allows you to reorder your results based on the data in one or more columns. First, take a look at how the table is ordered by default:
SELECT * FROM tutorial.billboard_top_100_year_end
Now let's see what happens when we order by one of the columns:
SELECT * FROM tutorial.billboard_top_100_year_end ORDER BY artist
You'll notice that the results are now ordered alphabetically from a to z based on the content in the
artist column. This is referred to as ascending order, and it's SQL's default. If you order a numerical column in ascending order, it will start with smaller (or most negative) numbers, with each successive row having a higher numerical value than the previous. Here's an example using a numerical column:
SELECT * FROM tutorial.billboard_top_100_year_end WHERE year = 2013 ORDER BY year_rank
If you'd like your results in the opposite order (referred to as descending order), you need to add the
SELECT * FROM tutorial.billboard_top_100_year_end WHERE year = 2013 ORDER BY year_rank DESC
You can also order by mutiple columns. This is particularly useful if your data falls into categories and you'd like to organize rows by date, for example, but keep all of the results within a given category together. This example query makes the most recent years come first but orders top-ranks songs before lower-ranked songs:
SELECT * FROM tutorial.billboard_top_100_year_end WHERE year_rank <= 3 ORDER BY year DESC, year_rank
You can see a couple things from the above query: First, columns in the
ORDER BY clause must be separated by commas. Second, the
DESC operator is only applied to the column that precedes it. Finally, the results are sorted by the first column mentioned (
year), then by
year_rank afterward. You can see the difference the order makes by running the following query:
SELECT * FROM tutorial.billboard_top_100_year_end WHERE year_rank <= 3 ORDER BY year_rank, year DESC
Finally, you can make your life a little easier by substituting numbers for column names in the
ORDER BY clause. The numbers will correspond to the order in which you list columns in the
SELECT clause. For example, the following query is exactly equivalent to the previous query:
SELECT * FROM tutorial.billboard_top_100_year_end WHERE year_rank <= 3 ORDER BY 2, 1 DESC
Note: this functionality (numbering columns instead of using names) is supported by Mode, but not by every flavor of SQL, so if you're using another system or connected to certain types of databases, it may not work.
ORDER BY with a row limit (either through the check box on the query editor or by typing in
LIMIT), the ordering clause is executed first. This means that the results are ordered before limiting to only a few rows, so if you were to order by
year_rank, for example, you can be sure that you are getting the lowest values of
year_rank in the entire table, not just in the first 100 rows of the table.
You can "comment out" pieces of code by adding combinations of characters. In other words, you can specify parts of your query that will not actually be treated like SQL code. It can be helpful to include comments that explain your thinking so that you can easily remember what you intended to do if you ever want to revisit your work. Commenting can also be useful if you want to test variations on your query while keeping all of your code intact.
You can use
-- (two dashes) to comment out everything to the right of them on a given line:
SELECT * --This comment won't affect the way the code runs FROM tutorial.billboard_top_100_year_end WHERE year = 2013
You can also leave comments across multiple lines using
/* to begin the comment and
*/ to close it:
/* Here's a comment so long and descriptive that it could only fit on multiple lines. Fortunately, it, too, will not affect how this code runs. */ SELECT * FROM tutorial.billboard_top_100_year_end WHERE year = 2013
Congrats on completing the Basic SQL tutorial!
You may find that your skills are limiting, though. If you want to do things like aggregate data across entire columns or merge multiple datasets together, check out the Intermediate SQL section of this tutorial.