How Can I Efficiently Generate Computed Columns in PostgreSQL for Faster Queries?

Optimizing PostgreSQL Queries with Computed Columns

For queries frequently accessing derived values from multiple tables, creating computed columns within the target table dramatically improves performance. PostgreSQL offers several methods to achieve this.

Views, while offering a logical representation of a query, aren't ideal for performance-critical scenarios because they don't physically store data.

A superior solution is PostgreSQL's "generated columns" (available from version 11 onwards). STORED generated columns store computed values directly within the table, providing the same performance as traditional columns.

For older PostgreSQL versions or situations where virtual generated columns aren't suitable, you can simulate computed columns using functions. These functions accept the table type as input and return the computed value, effectively acting as pseudo-columns.

Let's illustrate with an example:

CREATE TABLE tbl_a (a_id int, col1 int, col2 int);
INSERT INTO tbl_a VALUES (1,1,1), (2,2,2), (3,3,3), (4,4,4);

CREATE TABLE tbl_b (b_id int, a_id int, colx int);
INSERT INTO tbl_b VALUES
  (1,1,5),  (2,1,5),  (3,1,1)
, (4,2,8),  (5,2,8),  (6,2,6)
, (7,3,11), (8,3,11), (9,3,11);

To create a pseudo-column col3 using a function:

CREATE FUNCTION col3(tbl_a)
  RETURNS int8
  LANGUAGE sql STABLE AS
$func$
SELECT sum(colx)
FROM   tbl_b b
WHERE  b.a_id = .a_id
$func$;

Access the computed value using either attribute notation (tbl_a.col3) or functional notation (col3(tbl_a)), providing query flexibility. Remember to use table aliases to prevent naming conflicts.

Employing computed columns or generated functions minimizes subqueries, streamlining data retrieval and significantly boosting query speed. The best approach depends on your specific needs and PostgreSQL version. Careful consideration ensures efficient database design.

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