Query Primer - Column Aliases
(Page 4 of 4 )
Although the mysql tool will generate labels for the columns returned by your queries, you may want to assign your own labels. While you might want to assign a new label to a column from a table (if it is poorly or ambiguously named), you will almost certainly want to assign your own labels to those columns in your result set that are generated by expressions or built-in function calls. You can do so by adding a column alias after each element of your selectclause. Here’s the previous query against theemployeetable with column aliases applied to three of the columns:
mysql> SELECT emp_id,
-> 'ACTIVE' status,
-> emp_id * 3.14159 empid_x_pi,
-> UPPER(lname) last_name_upper
-> FROM employee;
| |
emp_id status empid_x_pi last_name_upper |
|
| 1 ACTIVE | 3.14159 SMITH | |
| 2 ACTIVE | 6.28318 BARKER | |
| 3 ACTIVE | 9.42477 TYLER | |
| 4 ACTIVE | 12.56636 HAWTHORNE | |
| 5 ACTIVE | 15.70795 GOODING | |
| 6 ACTIVE | 18.84954 FLEMING | |
| 7 ACTIVE | 21.99113 TUCKER | |
| 8 ACTIVE | 25.13272 PARKER | |
| 9 ACTIVE | 28.27431 GROSSMAN | |
| 10 ACTIVE | 31.41590 ROBERTS | |
| 11 ACTIVE | 34.55749 ZIEGLER | |
| 12 ACTIVE | 37.69908 JAMESON | |
| 13 ACTIVE | 40.84067 BLAKE | |
| 14 ACTIVE | 43.98226 MASON | |
| 15 ACTIVE | 47.12385 PORTMAN | |
| 16 ACTIVE | 50.26544 MARKHAM | |
| 17 ACTIVE | 53.40703 FOWLER | |
| 18 ACTIVE | 56.54862 TULMAN | |
|
18 rows in set (0.00 sec)
If you look at the column headers, you can see that the second, third, and fourth columns now have reasonable names instead of simply being labeled with the function or expression that generated the column. If you look at theselectclause, you can see how the column aliasesstatus,empid_x_pi, andlast_name_upperare added after the second, third, and fourth columns. I think you will agree that the output is easier to understand with column aliases in place, and it would be easier to work with programmatically if you were issuing the query from within Java or C# rather than interactively via the mysql tool.
Please check back next week for the continuation of this article.
| DISCLAIMER: The content provided in this article is not warranted or guaranteed by Developer Shed, Inc. The content provided is intended for entertainment and/or educational purposes in order to introduce to the reader key ideas, concepts, and/or product reviews. As such it is incumbent upon the reader to employ real-world tactics for security and implementation of best practices. We are not liable for any negative consequences that may result from implementing any information covered in our articles or tutorials. If this is a hardware review, it is not recommended to open and/or modify your hardware. |
|
 This article is excerpted from chapter three of the book Learning SQL, written by Alan Beaulieu (O'Reilly; ISBN: 0596007272). Check it out today at your favorite bookstore. Buy this book now.
|
|
/ 2 
