Database why use views

Views can also be used when you copy data to and from SQL Server to improve performance and to partition data. Besides the standard role of basic user-defined views, SQL Server provides the following types of views that serve special purposes in a database. Indexed Views An indexed view is a view that has been materialized. This means the view definition has been computed and the resulting data stored just like a table.

You index a view by creating a unique clustered index on it. Indexed views can dramatically improve the performance of some types of queries. Indexed views work best for queries that aggregate many rows.

They are not well-suited for underlying data sets that are frequently updated. Partitioned Views A partitioned view joins horizontally partitioned data from a set of member tables across one or more servers. This makes the data appear as if from one table. A view that joins member tables on the same instance of SQL Server is a local partitioned view. System Views System views expose catalog metadata.

You can use system views to return information about the instance of SQL Server or the objects defined in the instance. Sometimes, the execution speed of a query is so important that a developer is willing to trade increased disk space use for faster response, by creating a materialized view. Unlike the view discussed above, a materialized view does create and store the result table in advance, filled with data.

This technique is most useful when the query involves many joins of large tables, or any other SQL feature that could contribute to long execution times. Since the view would be useless if it is out of date, it must be re-run, at the minimum, when there is a change to any of the tables that it is based on. The SQL syntax to create a materialized view includes many options for when it is first to be run, how often it is to be re-run, and so on.

This requires an advanced reference manual for your specific system, and is beyond the scope of this tutorial. An index , as you would expect, is a data structure that the database uses to find records within a table more quickly. Indexes are built on one or more columns of a table; each index maintains a list of values within that field that are sorted in ascending or descending order. Rather than sorting records on the field or fields during query execution, the system can simply access the rows in order of the index.

Unique and non-unique indexes: When you create an index, you may allow the indexed columns to contain duplicate values; the index will still list all of the rows with duplicates. When you imagine to unit test SQL, views are the help. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow.

Learn more. When to use database views and when not? Ask Question. Asked 12 years, 8 months ago. Active 1 year, 2 months ago. Viewed 30k times. This question is about database views, not materialized-views. Pros: Query simplification. Avoid repeat the same joins on multiples queries. Avoid magic numbers.

Cons: Hiding real queries may be you are repeating joins. What else? Improve this question. FerranB FerranB Add a comment. Active Oldest Votes. Improve this answer. Andy White Andy White John Saunders John Saunders k 24 24 gold badges silver badges bronze badges. SingleNegationElimination SingleNegationElimination k 29 29 gold badges silver badges bronze badges. DevinB DevinB 8, 8 8 gold badges 42 42 silver badges 53 53 bronze badges.