Active Oldest Votes. Description as County from Application as a inner join Dictionary. Id inner join CountyCollaboration cc1 on co. CountyId inner join CountyCollaboration cc2 on cc1.
CollaborationId where c2. Improve this answer. Laurence Laurence Bogdan Bogdanov Bogdan Bogdanov 1, 2 2 gold badges 20 20 silver badges 31 31 bronze badges. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Podcast Making Agile work for data science. Stack Gives Back When we execute the following query, the query optimizer suggests a non-clustered index and it claims that this index dramatically improves the performance of the query.
As seen in the execution plan, the optimizer has decided to use a non-clustered index scan operator, and it reads data pages from the data cache. Now, we will apply the missing index suggestion. Without a doubt, the created index is used by the database engine and it boosts the performance of the query because the logical reads number is lower than the previous one.
The index seek operator details show us there is not any difference between the Actual Number of Rows and the Estimated Number of Rows.
This situation shows that the query optimizer finds accurate information about how many NULL rows are stored in the MiddleName column. Most likely, the following question will pop up in your mind. Basically, the statistics store the data distribution about the tables, and the query optimizer makes use of this information during the creation of a query plan.
When we create an index this data distribution information is also stored for the NULL valued columns. So that, optimizer estimates how much memory and other resources are required for a query. As we can see there is an number of NULL values are stored in the MiddleName column and this information is used by the query optimizer. In some cases, the ISNULL function is used with the where condition but this usage method may lead to use indexes inefficiently.
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