![]() However, when you try to unravel the views, for example by looking at the execution plan, the query turns out to be so complicated that it is almost impossible to understand what is really going on and how to improve it. Defining many layers of views so that your final queries look deceptively simple.There are two patterns of using views that tend to be problematic, and they both stem from the mistaken idea that a view works exactly like a table, just because it looks like one: Neither of these applications require you to “stack” views, that is, define views over views. They can be used as an interface to abstract from the actual table definitions, so that you can reorganize the tables without having to modify the interface.They allow you to have a recurring SQL query or expression in one place for easy reuse.Best practices with viewsīefore I show you how to untangle the mess, I’d like to tell you what mistakes to avoid when you are using views in your database design (excuse my switching to teacher mode I guess holding courses has that effect on you). You cannot create a view unless all the objects it requires are present. You first have to drop those views, then change the column and then run all the CREATE VIEW statements to create the views again.Īs the example shows, editing tables can be quite a challenge if there is a deep hierarchy of views, because you have to create the views in the correct order. However, you cannot do that if there are views that use the column. change a column’s data type from integer to bigint because you realize you will need to store bigger numbers. In this article I want to explore the mechanics behind view dependencies and show you how to track what views depend on a certain PostgreSQL object. Some people like it because it keeps the database consistent some people hate it because it makes schema modifications more difficult. CASCADE to drop the dependent objects too.ĮRROR: cannot drop column id of table t because other objects depend on itĭETAIL: view v depends on column id of table t ![]() This blog post explained different methods to modify a view in Postgres through practical examples.We all know that in PostgreSQL we cannot drop an object if there are view dependencies on it:ĮRROR: cannot drop table t because other objects depend on it The ALTER VIEW command allows us to alter/modify the view’s auxiliary properties. It creates a new view if it doesn’t exist already and modifies the view’s definition according to the specified query if it already exists. In Postgres, the “ CREATE OR REPLACE VIEW” command is used to modify the view’s definition. In Postgres, the “ ALTER VIEW” and “ CREATE OR REPLACE VIEW” statements are used to modify a view. The output snippet shows that the “example_view” has been modified successfully. For this purpose, we will use the ALTER VIEW statement as follows: ALTER VIEW example_view Suppose we want to rename a view from “ example_view” to “ sample_view”. We have already created a view named “example_view”, whose content is shown in the following snippet: Using the ALTER VIEW statement assists us in setting a default column, renaming a view, etc. How to Use ALTER VIEW Command in Postgres? The output snippet proves that the targeted view has been modified successfully. To verify the modified view, execute the “SELECT *” command: SELECT emp_id, emp_name, emp_salary, emp_age To do that, we will execute the CREATE OR REPLACE view statement as follows: CREATE OR REPLACE VIEW emp_view AS Suppose we want to modify the “emp_view” according to the “emp_bio” table. We have also created a sample table whose structure is shown in the below snippet: We have created a sample view named “emp_view,” whose data is shown in the following snippet: And it will modify the view’s definition according to the specified query if it already exists. The create or replace command will create a new view if it doesn’t exist already. Use the following syntax to use the “ CREATE OR REPLACE VIEW” statement in Postgres: CREATE OR REPLACE name_of_view How to Use CREATE OR REPLACE VIEW Command in Postgres? In this tutorial, we will show you how to alter a view in Postgres to modify the definition of a view. Postgres offers various commands to work with views, such as CREATE VIEW, DROP VIEW, etc. A VIEW in Postgres enables us to define a SELECT statement as a named object, which can be used to query data just like a regular table. In PostgreSQL, a view is a virtual table that is based on a SELECT query.
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