It is not possible to create an index on a view. Indexes can be used for views processed using the merge algorithm. However, a view that is processed with the temptable algorithm is unable to take advantage of indexes on its underlying tables (although indexes can be used during generation of the temporary tables).
Can indexes be created on views?
Indexes can only be created on views which have the same owner as the referenced table or tables. This is also called an intact ownership-chain between the view and the table(s). Typically, when table and view reside within the same schema, the same schema-owner applies to all objects within the schema.
Why MySQL do not use index?
3 Answers. MySQL will not use the index if it estimates that it would select a significantly large portion of the table, and it thinks that a table-scan is actually more efficient in those cases.
Can MySQL combine indexes?
Yes, MySQL can use multiple index for a single query. The optimizer will determine which indexes will benefit the query. You can use EXPLAIN to obtain information about how MySQL executes a statement.
Can we have indexes on views in SQL Server?
To enhance the performance of such complex queries, a unique clustered index can be created on the view, where the result set of that view will be stored in your database the same as a real table with a unique clustered index. …
How do I view indexes in SQL Developer?
To view indexes:
- In the Connections navigator in SQL Developer, navigate to the Indexes node for the schema that includes the index you want to view. If the index is in your own schema, navigate to the Indexes node in your schema. …
- Open the Indexes node. …
- Click the name of the index you want to view.
How does MySQL choose index?
If there is a choice between multiple indexes, MySQL normally uses the index that finds the smallest number of rows (the most selective index). If the table has a multiple-column index, any leftmost prefix of the index can be used by the optimizer to look up rows.
Can we avoid index by using hint?
Suppose you want to use a specific index for your query to avoid a table scan, we can use table hints. One of the popular table hints is WITH(NOLOCK) to avoid default transaction isolation level and avoid locking issues in Select statements.
How do I create an index column in MySQL?
To create indexes, use the CREATE INDEX command: CREATE INDEX index_name ON table_name (column_name); You can an index on multiple columns.
Does index order matter MySQL?
So the order of columns in a multi-column index definitely matters. One type of query may need a certain column order for the index. If you have several types of queries, you might need several indexes to help them, with columns in different orders.
Can SQL use multiple indexes?
Yes, two indexes may be used when 1st WHERE condition is covered by Index1 and 2nd WHERE condition is covered by Index2. In this case SQL may decide to use Index Seek for both indexes and then do Hash Match (Inner Join).
How many indexes can MySQL use?
In general, MySQL only allows you to create up to 16 indexes on a given table. If you are using a PRIMARY KEY index, you can only have one primary key per table.
Do views improve performance SQL Server?
Views make queries faster to write, but they don’t improve the underlying query performance. … In short, if an indexed view can satisfy a query, then under certain circumstances, this can drastically reduce the amount of work that SQL Server needs to do to return the required data, and so improve query performance.
Does MySQL have materialized views?
A Materialized View (MV) is the pre-calculated (materialized) result of a query. Unlike a simple VIEW the result of a Materialized View is stored somewhere, generally in a table. … MySQL does not provide Materialized Views by itself.
Can indexes be created on views in Oracle?
Oracle SQL standards do not support creating indexes on views. If you need to index documents whose contents are in different tables, you can create a data storage preference using the USER_DATASTORE object.