oracle modify view

A view in Oracle database is a virtual table, which is composed of the query results of one or more basic tables. Views simplify query statements and allow users to view only specific columns and rows of data. However, in practical applications, the view needs to be modified to meet specific needs. This article will introduce how to modify views in Oracle database.

1. Syntax for modifying the view

Use the ALTER VIEW statement to modify an existing view. The ALTER VIEW syntax is:

ALTER VIEW view_name [options];

Among them, view_name is the name of the view to be modified, and options are used to specify the attributes of the view to be modified. The options parameter list is as follows:

1. CHECK OPTION

The CHECK OPTION option is used to limit the set of rows that can be modified in INSERT, UPDATE, and DELETE statements. This option can be specified with:

ALTER VIEW view_name CHECK OPTION;

2. FORCE/NO FORCE

The FORCE option instructs Oracle to force the use of new efficiencies A higher interpreter to execute statements in this view. This option can be specified by:

ALTER VIEW view_name FORCE|NO FORCE;

3. COMPILE/NO COMPILE

The COMPILE option instructs Oracle to recompile view. This option can be specified by:

ALTER VIEW view_name COMPILE|NO COMPILE;

4. OPTIMIZE

The OPTIMIZE option instructs Oracle to optimize the view. This option can be specified in the following way:

ALTER VIEW view_name OPTIMIZE;

2. Example of modifying the view

The following is an example of modifying the view:

1. Modify the check options of the view

Assume the following view definition:

CREATE VIEW view_emp
AS
SELECT *
FROM emp
WHERE salary > 5000

Suppose we want to protect this view so that only employees with a salary greater than 5000 can be inserted into this view. We can use the CHECK OPTION option to limit modifications:

ALTER VIEW view_emp CHECK OPTION;

Now, if we try to insert an employee record less than or equal to 5000 into this view, we will Received an error message.

2. Modify the mandatory options of the view

Now assume that there is the following view definition:

CREATE VIEW view_dept
AS
SELECT d.dept_no, d.dept_name , e.emp_name
FROM dept d, emp e
WHERE d.dept_no = e.dept_no

Suppose we want to force Oracle to use a new interpreter to execute statements in this view. We can use the FORCE option to achieve this:

ALTER VIEW view_dept FORCE;

Now, Oracle will use a new interpreter to execute the view, which may improve the execution efficiency of the view.

3. Recompile the view

If we modify the structure of the view's underlying table, then we need to recompile the view to ensure that it is in sync with the underlying table.

The following is an example of recompiling a view:

ALTER VIEW view_emp COMPILE;

This will force Oracle to recompile the view to ensure that it remains in sync with the underlying tables.

4. Optimize the view

If we need to optimize a view, we can use the OPTIMIZE option.

The following is an example of optimizing a view:

ALTER VIEW view_emp OPTIMIZE;

This will tell Oracle to optimize the view to improve its execution efficiency.

Summary:

This article introduces how to modify views in Oracle database. Use the ALTER VIEW statement to modify the view's properties, check options, force options, recompile and optimization options. In the application, we can use these options to meet specific application needs and improve the execution efficiency of the view.

The above is the detailed content of oracle modify view. For more information, please follow other related articles on the PHP Chinese website!