ALTER VIEW - MySQL

Overview

ALTER VIEW alters the definition of an existing view in the current database. It allows you to modify the view’s query, add or remove columns, or change the underlying tables involved.

Syntax

ALTER VIEW view_name
    [AS | ALGORITHM={UNDEFINED|MERGE|TEMPTABLE}]
    select_statement
    [WITH [CASCADED | LOCAL] CHECK OPTION]

Options/Flags

• AS | ALGORITHM={UNDEFINED|MERGE|TEMPTABLE}: Specifies the algorithm used to evaluate the view.
  • UNDEFINED: MySQL chooses an algorithm based on the query.
  • MERGE: Uses a merge algorithm, which is suitable for simple queries.
  • TEMPTABLE: Uses a temporary table algorithm, which is more efficient for complex queries.
• WITH CASCADED | LOCAL CHECK OPTION: Specifies whether to enforce referential integrity constraints on the view.
  • CASCADED: Enforces constraints on both the view and the underlying tables.
  • LOCAL: Enforces constraints only on the view.

Examples

Example 1: Modifying the query of a view:

ALTER VIEW my_view AS
SELECT id, name, age
FROM users
WHERE age > 18;

Example 2: Adding a column to a view:

ALTER VIEW my_view
ADD COLUMN full_name VARCHAR(255);

Common Issues

• View not found: Ensure that the view being altered exists in the current database.
• Invalid query: The query used to define the view must be syntactically correct and reference existing tables and columns.
• Referential integrity violations: When using WITH CASCADED CHECK OPTION, ensure that the view’s constraints are compatible with the underlying tables.

Integration

ALTER VIEW can be used in conjunction with other commands to manage views efficiently. For example:

• CREATE VIEW: Creates a new view.
• DROP VIEW: Deletes an existing view.
• SELECT FROM view_name: Queries a view like a regular table.

Related Commands

• CREATE VIEW: Defines a new view.
• DROP VIEW: Removes a view from the database.
• SHOW CREATE VIEW: Displays the definition of a view.