MySQL - ALTER VIEW Statement



MySQL ALTER VIEW Statement

A MySQL view is a composition of a table in the form of a predefined SQL query. It is stored in the database with an associated name.

You can change the definition of an existing view using the ALTER VIEW Statement

Syntax

Following is the syntax of the ALTER VIEW Statement −

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

Example

Suppose we have created a table named dispatches_data using the CREATE statement as shown below −

CREATE TABLE dispatches_data(
   ProductName VARCHAR(255),
   CustName VARCHAR(255),
   DispatchTimeStamp timestamp,
   Price INT,
   Location VARCHAR(255)
);

Now, let us insert some records into the dispatches_data table −

Insert into dispatches_data values
('Key-Board','Raja',TIMESTAMP('2019-05-04','15:02:45'),7000,'Hyderabad'),
('Earphones','Roja',TIMESTAMP('2019-06-26','14:13:12'),2000,
'Vishakhapatnam'),
('Mouse','Puja',TIMESTAMP('2019-12-07','07:50:37'), 3000,'Vijayawada'),
('Mobile','Vanaja',TIMESTAMP ('2018-03-21','16:00:45'),9000,'Chennai'),
('Headset','Jalaja',TIMESTAMP('2018-12-30','10:49:27'),6000,'Goa')

Let us create a view using the CREATE VIEW statement as shown below −

CREATE VIEW testView AS SELECT * FROM dispatches_data;

You can retrieve the definition of the above created view using the SHOW CREATE VIEW statement as shown below −

SHOW CREATE VIEW testView;

Output

The above query produces the following output −

*************** 1. row ***************
                View: testview
         Create View: CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` 
		              SQL SECURITY DEFINER VIEW `testview` AS select 
					  `dispatches_data`.`ProductName` AS `ProductName`,
					  `dispatches_data`.`CustName` AS `CustName`,
					  `dispatches_data`.`DispatchTimeStamp` AS 
					  `DispatchTimeStamp`,`dispatches_data`.`Price` AS 
					  `Price`,`dispatches_data`.`Location` AS `Location` 
					  from `dispatches_data`
character_set_client: cp850
collation_connection: cp850_general_ci

Following query alters the ALGORITHM of the table −

ALTER ALGORITHM=MERGE VIEW testView AS SELECT * FROM dispatches_data;

Verification

If you retrieve the definition of the above created view after altering the table you can observe the name of the algorithm −

SHOW CREATE VIEW testView;

Once the query is executed, it will generate the following output −

*************** 1. row ***************
                View: testview
         Create View: CREATE ALGORITHM=MERGE DEFINER=`root`@`localhost` 
		              SQL SECURITY DEFINER VIEW `testview` AS select 
					  `dispatches_data`.`ProductName` AS `ProductName`,
					  `dispatches_data`.`CustName` AS `CustName`,
					  `dispatches_data`.`DispatchTimeStamp` AS 
					  `DispatchTimeStamp`,`dispatches_data`.`Price` AS 
					  `Price`,`dispatches_data`.`Location` AS `Location` 
					  from `dispatches_data`
character_set_client: cp850
collation_connection: cp850_general_ci

Altering an existing view based on columns

If a view is created such that it includes all (or certain) columns of a table you can change the columns used in the view using the ALTER VIEW statement.

Syntax

ALTER VIEW view_name column_list AS select_statement;

Example

If you retrieve the contents of the above created view using SELECT statement as shown below −

SELECT * FROM testView;

Output

Following is the output of the above query −

ProductName CustName DispatchTimeStamp Price Location
Key-Board Raja 2019-05-04 15:02:45 7000 Hyderabad
Earphones Roja 2019-06-26 14:13:12 2000 Vishakhapatnam
Mouse Puja 2019-12-07 07:50:37 3000 Vijayawada
Mobile Vanaja 2018-03-21 16:00:45 9000 Chennai
Headset Jalaja 2018-12-30 10:49:27 6000 Goa

Following query alters the columns of an existing views −

ALTER VIEW testView (ProductName, Price, Location) AS 
SELECT ProductName, Price, Location FROM dispatches_data;

Verification

You can verify the contents of altered view as shown below −

SELECT * FROM testView;

After executing the above query, it produces the following output −

ProductName Price Location
Key-Board 7000 Hyderabad
Earphones 2000 Vishakhapatnam
Mouse 3000 Vijayawada
Mobile 9000 Chennai
Headset 6000 Goa
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