Pass In “WHERE” parameters to PostgreSQL View?

Question

I have a rather complicated query on my PostgreSQL database spanning 4 tables via a series of nested subqueries. However, despite the slightly tricky looking appearance and

Answer 1

In addition to what @a_horse already cleared up, you could simplify your SQL by using JOIN syntax instead of nested subqueries. Performance will be similar, but the syntax is much shorter and easier to manage.

CREATE OR REPLACE FUNCTION param_labels(_region_label text, _model_label text)
  RETURNS TABLE (param_label text, param_graphics_label text) AS
$func$
    SELECT p.param_label, p.param_graphics_label
    FROM   parameters      p 
    JOIN   parameter_links l USING (param_id)
    JOIN   regions         r USING (region_id)
    JOIN   models          m USING (model_id)
    WHERE  p.active
    AND    r.region_label = $1 
    AND    m.model_label = $2
    ORDER  BY p.param_graphics_label;
$func$ LANGUAGE sql;

• If model_label is not unique or something else in the query produces duplicate rows, you may want to make that SELECT DISTINCT p.param_graphics_label, p.param_label - with a matching ORDER BY clause for best performance. Or use a GROUP BY clause.

• Since Postgres 9.2 you can use the declared parameter names in place of $1 and $2 in SQL functions. (Has been possible for PL/pgSQL functions for a long time).

• Care must be taken to avoid naming conflicts. That's why I make it a habit to prefix parameter names in the declaration (those are visible most everywhere inside the function) and table-qualify column names in the body.

• I simplified WHERE p.active = 'TRUE' to WHERE p.active, because the column active should most probably be of type boolean, not text.

• USING only works if the column names are unambiguous across all tables to the left of the JOIN. Else you have to use the more explicit syntax:
  ON l.param_id = p.param_id