A database view is a virtual table which is defined as a SQL select query with JOIN statement. Same as database table it consists of rows and columns.
When any data of a tables changes, the corresponding view reflects that changes as well.
Advantages:
Disadvantages:
Simple view example:
CREATE VIEW userOrder AS SELECT userID, orderID SUM (qty * price) total FROM orders GROUP by orderID ORDER BY total DESC
You can also use JOIN and sub-query to the view.
Once a view created in a database, you can remove it by using the DROP VIEW statement:
DROP VIEW [IF EXISTS] userOrder
After a view is defined, you can modify it by using the ALTER VIEW statement:
ALTER VIEW userOrder AS SELECT userID, orderID, discount_amount SUM (qty * price) total FROM orders GROUP by orderID ORDER BY total DESC
To create a updateable views you need to consider following things:
UPDATE userOrder SET total = 2250 WHERE userID = 5 AND orderID = 135
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