How do I return row numbers with my query?
Often, people want to "invent" an identity, or rank, on the fly. So their original result set would look like this:
And they would want this:
This would act like Oracle's ROWNUM, which isn't supported in SQL Server.
Of course, once you've retrieved this resultset into your ASP page, you could use a counter to increment as you're processing. This is by the easiest way, e.g.
However, some people really, really, really want the row number to come back from the database. It's a little less efficient, but let's examine a few methods. Given this sample data:
The first method we'll try is a COUNT with a GROUP BY:
We can also try a COUNT as a subquery, which doesn't require GROUP BY (which means you could include other columns in the outer query).
Results in all cases:
Note that if you have duplicates in your table, you will end up with something like this:
So, to avoid this, you might want to make sure that either (a) you avoid and remove duplicates (see Article #2431); or (b) if duplicates are allowed and make sense for your data model, that you have some other primary key or unique identifier. Then, you can make it a part of the query; for example:
Grouping within groups
Often, you'll want a more complex row number scheme, for example you might want to rank within groups of a hierarchy. Let's say we wanted to list sports teams, and assign "ranks" alphabetically, within each city:
Keep in mind that, since your presentation tool (Crystal Reports, ASP, PHP, what have you) is going to have to treat every row separately anyway, it makes sense to just retrieve the rows in the correct order, and let the application compare every row to see if this is a new city or not, and accordingly increment the count or start over. This will greatly reduce the amount of strain you're putting on the database.
Be sure to read KB #186133 for Microsoft's official word, and this article for a variety of approaches from Greg Larsen.
There is also a great article by Itzik Ben-Gan available for registered users of SQL Server Magazine's web site:
Windows Article - Welcome
And thanks to Hugo Kornelis for pointing out an error based on my choice of names! Since the first letter of all of the first names I chose was alphabetically lower than each corresponding last name, I hadn't noticed that the results could be skewed in some of the above queries, if you added a name like Jason Arnott. I believe I have corrected this, but have deferred re-populating the results above for now. Please let us know if you find any issues...
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