Oracle sequence, view, index

Sequence

Created in sequences

Role

Generate an auto-grow (or decrease) integer value

Use when adding data frequently, controllability is good

notation: sequence name. Nextval Gets the next sequence value

The sequence name. Currval Gets the current sequence value, not commonly used.

View

Virtual tables defined on the basis of physical tables

Create in views

Role:

The complex query logic is saved in the form of view, which facilitates the reuse of query results.

Generally used to query data, not to do data updates

Commonly used for compatibility or migration of systems

Views cannot be indexed and are suitable for query statements with small amounts of data

Create a View

Wording: SELECT * from view name

Materialized view

Physical storage of data in a normal view

You can create indexes that are suitable for query statements with large data volumes

However, the data is not synchronized with the original table and needs to be refreshed.

Created in materialized views

There will be one more table in the tables after creation.

Refresh Statement

In the command window, create

exec Dbms_mview.refresh (' Physical View name ')

Index

One way to improve query efficiency

Auto Create: Automatically created based on primary key or uniqueness constraint

Manually created: The data values in the column are distributed in a wide range

Columns often appear in a WHERE clause or join condition

Tables are frequently accessed and data volumes are large

Tables are not updated frequently

Features: The order of indexed columns is consistent with the order of the columns of the query criteria, increasing the index hit ratio. Indexes can affect the efficiency of data updates, not multiple builds.

Create a method

Oracle sequence, view, index