How to Create Virtual Tables in PostgreSQL using `setof record`?

Creating Virtual Tables with setof record in PostgreSQL

This article delves into creating virtual tables using the setof record approach in PostgreSQL. A virtual table does not have its own underlying data storage; instead, it is a temporary data representation based on passed parameters or calculations.

To create a virtual table that returns three columns and an unknown number of rows, utilize the following PL/pgSQL function:

CREATE OR REPLACE FUNCTION f_foo()
  RETURNS TABLE (a int, b int, c int) AS
$func$
BEGIN
RETURN QUERY VALUES
  (1,2,3)
, (3,4,5)
, (3,4,5)
;
END
$func$  LANGUAGE plpgsql IMMUTABLE ROWS 3;

This function uses the RETURNS TABLE clause to define the row type returned by the function. The RETURN QUERY command generates multiple rows using a VALUES expression. The IMMUTABLE and ROWS 3 clauses optimize the function for performance.

To invoke the virtual table, simply call the function:

SELECT * FROM f_foo();

Additionally, you can construct virtual tables using a plain SQL statement:

VALUES (1,2,3), (3,4,5), (3,4,5)

For more complex cases, define column names and types:

SELECT *
FROM  (
   VALUES (1::int, 2::int, 3::int)
        , (3, 4, 5)
        , (3, 4, 5)
   ) AS t(a, b, c);

Finally, encapsulate the virtual table creation into a SQL function:

CREATE OR REPLACE FUNCTION f_foo()
   RETURNS TABLE (a int, b int, c int) AS
$func$
   VALUES (1, 2, 3)
        , (3, 4, 5)
        , (3, 4, 5);
$func$  LANGUAGE sql IMMUTABLE ROWS 3;

By implementing these approaches, you can effectively create virtual tables in PostgreSQL, enabling flexibility and customization in data processing.

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