Cost of updating secondary indices best punk dating sites
This is the cost to SQL Server to execute the query.The lower the number the less resource intensive for SQL Server.
From a simple standpoint SQL Server offers two types of indexes clustered and non-clustered.In this query we are only requesting column lastname. From this output you can see that the RID Lookup has been replaced with a Clustered Index Seek. So based on these examples you can see the benefits of using indexes.Since this query can be handled by just the non-clustered index (covering query), SQL Server does not need to access the actual data pages. Overall it is the same type of operations, except using the Clustered Index. This example table only had 20,000 rows of data, so this is quite small compared to most database tables.In its simplest definition a clustered index is an index that stores the actual data and a non-clustered index is just a pointer to the data.
A table can only have one Clustered index and up to 999 Non-Clustered Indexes (depending on SQL version).If a table does not have a clustered index it is referred to as a Heap. To further clarify, lets take a look at what indexes do and why they are important.