Zero, One, Close Enough

Kendra Little points out a columnstore optimization which leaves a strange execution plan as a result:

I have a very simple query. It’s running against a table with a nonclustered columnstore index.

SELECT COUNT(*) FROM pt.FirstNameByBirthDate_1966_2015;

GO

The query returns one row, as expected. Here’s my count:

For the record, that is the correct number of rows in the table. Here’s where things get weird. In the actual execution plan, the columnstore index returns zero rows.

Yes, this is really the actual execution plan. I’m not tricking you, I promise.

Click through for the answer.

Related Posts

Cloning And Columnstore Statistics

Niko Neugebauer points out a fix in SQL Server 2019: I have a huge love for the DBCC CLONEDATABASE command – it has been made available (backported) to every SQL Server version starting with SQL Server 2012, since the original release in SQL Server 2014, while being constantly improved in the Service Packs and Cumulative Updates. This […]

Read More

Hybrid Columnstore And B+ Tree Designs

Adrian Colyer reviews a Microsoft paper on the combination of columnstore and B+ tree indexes on a single table: The authors conducted a series of microbenchmarks as follows: scans with single predicates with varying selectivity to study the trade-off between the range scan of a B+ tree vs a columnstore scan sort and group-by queries […]

Read More

Categories

March 2017
MTWTFSS
« Feb Apr »
 12345
6789101112
13141516171819
20212223242526
2728293031