Views and Functions in PostgreSQL

Views and Functions in PostgreSQL streamline SQL query management, with Views suited for fixed queries and Functions offering flexibility through parameter support.


Views

A View is a virtual table that stores an SQL query. It does not occupy disk space and always returns real-time data based on the stored query. However, Views do not allow the use of parameters, which limits their flexibility.

Example of a View to summarize client data:

CREATE VIEW client_summary AS (

SELECT client.id, client.name, client.contact, client_amount.total

FROM client

JOIN (

SELECT sale.client_id, SUM(sale.amount) AS total 

FROM sale 

GROUP BY sale.client_id

) AS client_amount 

ON client.id = client_amount.client_id

WHERE client.id = 1

);

This View works only for a fixed client ID. In this case, 1.


Functions

Functions provide greater flexibility, accepting parameters and using the PL/pgSQL language. They can return values of different types, such as tables.

Example of a Function that returns client data based on a provided ID:

CREATE FUNCTION client_summary(client_id INT) RETURNS TABLE(id INT, name TEXT, contact TEXT, total DECIMAL(10, 2)) AS $$

DECLARE 

BEGIN

RETURN QUERY

SELECT client.id, client.name, client.contact, client_amount.total

FROM client

JOIN (

SELECT sale.client_id, SUM(sale.amount) AS total

FROM sale

GROUP BY sale.client_id

) AS client_amount

ON client.id = client_amount.client_id

WHERE client.id = $1;

END;

$$ LANGUAGE PLPGSQL;

Query for any client:

SELECT * FROM client_summary(1);


Use Views for fixed queries and Functions for dynamic queries.

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