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What is the impact of table scan on performance?


Posted by: James
On 25 Mar 2012 | Views: 809 | Categories: Database (SQL Server)
Interview Answers(1)

 On 25 Mar 2012 10:53:10 AM
When a SQL Server has no index to use for searching, the result is similar to the reader who looks at every page in a book to find a word. The SQL engine needs to visit every row in a table.

In database terminology we call this behavior a table scan, or just scan. A full table scan of a very large table can adversely affect the performance. Creating proper indexes will allow the database to quickly narrow in on the rows to satisfy the query, and avoid scanning every row in the table.

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