How fast sql count

When doing a count aggregate SQL query, what can speed up the execution time in these 3 database systems? I'm sure many things could speed it up hardware for one , but I'm just a novice DBA, so I'm sure I'll be getting a few answers here.

I migrated about million rows to a SQL Server database, and this query is taking forever. But in my source Netezza database, it takes seconds. Netezza is an appliance that is designed to excel at large table scans, so that's why you're getting such fast results on that system.

For your SQL Server, you can greatly speed up the row count by querying from the sys. But from your question, it sounds like you are just doing row counts to verify each table after your migration, so this query should work for you. This will get you a transactionally-consistent count without the overhead of big table or index scans, and without the need for the storage required for the latter:.

This will require a single initial scan no getting away from this , and add a bit of overhead to incremental table data manipulations. If you're doing big operations with lots of data as opposed to many small operations , I think the overhead on changes should be negligible.

However, a regular binary tree index will still be huge with Mrows. If your table is not updated concurrently ie. Null entries are taken into account by a bitmap index. The resulting index will be tiny 8k blocks per million row compared to either a regular binary tree index or the base table. If your table is updated concurrently, a bitmap index with a unique value will be a point of contention and shouldn't be used.

In Oracle, simple count query is often executed by scanning an index instead of whole table. For more complex queries that require full table scan, you could use parallel query. Sign up to join this community. The best answers are voted up and rise to the top.

Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? COUNT 1 vs. There are more efficient ways than using the COUNT function if the goal is just to retrieve the total row count from a table.

One way is to retrieve the row count directly from SQL Server sys. SQL Server is actually pretty smart as it can choose an efficient route to get the record count. In this case, there is a clustered index and a non-clustered index which does not allow NULL. SQL Server performs a count on the column using the clustered index.

Typically, you would want to create a nonclustered index here, so that SQL Server would be able to perform a scan on a smaller index. I realize that I'm a bit late to this thread but you've not actually proven your conclusion of no performance advantage because you've not actually measured CPU usage, duration, reads, or writes. Do you see a lot of users doing row count checks? I am tired atm so maybe I am missing an extrapolation to real world stuff. Simon — yep, thus the post.

This stemmed from a client use case. I try to share as much as I can here, though. The speed of columnstore is unparalleled, but feels like index creation time has to be included for a fair comparison. Yes, the point of this entire post — as one might guess from the title — was to make the relevant queries fast.

Not everyone might gather that, though. Thanks Brent…learned something new. Could you do another blog on this new way of counting as well?

I would be interested in your opinion on use cases for it. Martin — ah no, counting distincts even the new approx function is way slower than just counting the number of rows. I hate stuff like that. Your email address will not be published. Don't subscribe All Replies to my comments Notify me of followup comments via e-mail. You can also subscribe without commenting. Post Comment.