In this lesson you are going to explore how to sort your query results by using SQL’s ORDER BY statement. Using this phrase allows us to sort our result in ascending or descending order. In addition you can limit your query to a specified number of results. The lesson’s objectives are to:
- learn how to sort on one column in ascending or descending order
- sort on two or more columns
- sort on a calculated field
- limit our query to a specified number of results
Once you have gone through the lesson, please be sure to do the exercises. These and the examples that follow are based on the sample database. Be sure to get a copy so you can follow along.
In order to sort a query’s results use the ORDER BY clause. This clause comes after the FROM clause and is where you specify columns or expression to use to order your data. When using the ORDER BY clause the select statement takes the form
SELECT columns FROM table ORDER BY columns;
So if you wanted to sort employees by last name you could state
SELECT FirstName, LastName FROM Employees ORDER BY LastName;
In addition you can specify the direction to sort. Unless specified, all sorts are in ascending order (smallest to largest) and can be explicitly specified using the ASC keyword
SELECT FirstName, LastName FROM Employees ORDER BY LastName ASC;
To sort by LastName in descending order you would issue the statement
SELECT FirstName, LastName FROM Employees ORDER BY LastName DESC;
DESC stand for Descending.
ORDER BY More than One Column
You can also order by more than one column. Just separate the columns you wish to sort with a comma. If you wanted to sort OrderDetails by Quantity and UnitPrice enter
SELECT ProductID, Quantity, UnitPrice FROM OrderDetails ORDER BY Quantity, UnitPrice;
You can also specify the sort order, that is whether the columns are sorted in ascending or descending order. In this sample the OrderDetails are sorted in descending order by price within quantity.
SELECT ProductID, Quantity, UnitPrice FROM OrderDetails ORDER BY Quantity ASC, UnitPrice DESC;
ORDER BY A Calculated Value
So far you have learned to sort on one or more columns, but did you know you can sort on a expression? For instance, consider OrderDetails, perhaps you would like to know who has largest orders. Of course you can sort by Quantity or UnitPrice, but what about TotalPrice? That column doesn’t exist in the table, be we learned how to create it as a an expression in our last lesson. Can we sort on this? Sure! Check out the following, and look closely at the ORDER BY clause, there you’ll see where it’s ordered by TotalPrice (UnitPrice * Quantity)
SELECT ProductID, Quantity, UnitPrice FROM OrderDetails ORDER BY UnitPrice * Quantity;
To make it more clear, lets also display the TotalPrice
SELECT ProductID, Quantity, UnitPrice, UnitPrice * Quantity AS TotalPrice FROM OrderDetails ORDER BY UnitPrice * Quantity;
And here is where aliasing, or renaming fields, can help. Here UnitPrice * Quantity is aliased as TotalPrice in the SELECT clause. Now that’s done, we can simply refer to TotalPrice when specifying the sort order.
SELECT ProductID, Quantity, UnitPrice, UnitPrice * Quantity AS TotalPrice FROM OrderDetails ORDER BY TotalPrice;
The last item I would like to go over with you is being able to limit the number of sorted results returned from a list. This makes it really easy to return the “first ten” or “top ten” items in a search. For instance if you want to know the top five orderdetail items, you could enter the following query into SQLite
SELECT ProductID, Quantity, UnitPrice, UnitPrice * Quantity AS TotalPrice FROM OrderDetails ORDER BY TotalPrice LIMIT 5;
The LIMIT keyword limits our search to the first five rows. You can limit by other numbers of course, in fact you can also limit by any number resulting from an expression. Tip! To get the last five rows of a result, such as the smallest five orders, just order your result in descending order.
It’s important to practice! Use the sample database to answer these questions.
- Write a statement to select customer names, cities, and stated, sorted by customer’s cities.
- Write a statement to select employee first and last names ordered by the upper case equivalent of their last name. Remember: We discussed UPPER in the previous lesson.
- Select the first two names to appear in a sort of employee last names.
- Select the last two names to appear in a sort of employee last names.
Answers to the Exercises
Congratulations! You just learned how to use the select command to query a database. More tutorials are to follow! Remember! I want to remind you all that if you have other questions you want answered, then post a comment or tweet me. I’m here to help you. What other topics would you like to know more about?