What is the difference between scan and seek?
What is the difference between scan and seek?
An index scan or table scan is when SQL Server has to scan the data or index pages to find the appropriate records. A scan is the opposite of a seek, where a seek uses the index to pinpoint the records that are needed to satisfy the query.
What is the difference between a full table scan and an index scan?
Table scan means iterate over all table rows. Index scan means iterate over all index items, when item index meets search condition, table row is retrived through index. Usualy index scan is less expensive than a table scan because index is more flat than a table. They are lot of bibliografy about this issue.
What is the difference between table scan and index scan?
Table scan means iterate over all table rows. Index scan means iterate over all index items, when item index meets search condition, table row is retrived through index. Usualy index scan is less expensive than a table scan because index is more flat than a table.
How do you optimize a query in SQL Server?
It’s vital you optimize your queries for minimum impact on database performance.
- Define business requirements first.
- SELECT fields instead of using SELECT *
- Avoid SELECT DISTINCT.
- Create joins with INNER JOIN (not WHERE)
- Use WHERE instead of HAVING to define filters.
- Use wildcards at the end of a phrase only.
How do I improve my Clustered index scan?
3 Answers
- don’t use SELECT * – that’ll always have to go back to the clustered index to get the full data page; use a SELECT that explicitly specifies which columns to use.
- if ever possible, try to find a way to have a covering nonclustered index, e.g. an index that contains all the columns needed to satisfy the query.
What is the difference between index full scan and index fast full scan?
Answer: While an index fast full scan reads all of the data block in the index, in data block order, and index full scan does not read all of the blocks in an index. Also, a fast-full scan reads the data blocks in block sequence, while an index full scan reads the index in tree order.
