Cardinality Estimates

External Article

Fixing Gatekeeper Row Cardinality Estimate Issues

  • Article

The Query Optimiser needs a good estimate of the number of rows likely to be returned by each physical operator in order to select the best query plan from the most likely alternatives. Sometimes these estimates can go so wildly wrong as to result in a very slow query. Joe Sack shows how it can happen with SQL Queries on a data warehouse with a star schema.

2012-12-10

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Question of the Day

Using table variables in T-SQL

What happens if you run the following code in SQL Server 2022+? 

declare @t1 table (id int);

insert into @t1 (id) values (NULL), (1), (2), (3);

select count(*)
from @t1
where @t1.id is distinct from NULL;
 

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